(FORTUNE Magazine) – THE RENAISSANCE comes to mind when a Democratic congressional leader looks ahead to next year. He is thinking not of glorious painting or of sublime poetry, but of the legendary poisoned cup at a Borgia banquet. This lawmaker figures that if Governor Dukakis becomes president, he will have troubles aplenty, from the budget deficit on down. The Republicans on Capitol Hill, he says, will delight in Dukakis's predicament without lifting a finger to help: ''You have won the crown. Enjoy it.'' The Democrats may be just as spiteful should Vice President Bush win. The 101st Congress, which convenes in January, could be the most sullen and belligerent in years. And the most powerful as well. So far, neither Bush nor Dukakis has been able to generate the kind of voter enthusiasm -- a mandate -- that helped President Reagan dominate Congress early in his Administration. Several committees that have considerable impact on business, including the Senate Banking and the House Judiciary, will get new chairmen. Otherwise, the faces of the next Congress, though grimmer, will be mostly the same as those of the outgoing 100th. The government's No. 1 running crisis -- the deficit -- will also be staying around, and the chances for a resolution don't look good. Democrats will almost certainly stay in command. In the House, which has not been governed by Republicans since 1952, the call won't even be close. Democrats currently outnumber Republicans 255 to 177, and even if the nation's political inclination were to shift radically right or left, the ratio would not change much. By a sort of Newtonian law, a body that comes to rest in Congress these days tends to remain there until he or she dies or quits. Seventy incumbents face no challenger at all. For another 300 or so, their races will be no more than aerobic walks, according to the calculations of Brookings Institution scholar Thomas Mann. Those 300 will keep their jobs partly because they pay close attention to their constituents, but more importantly because they have the support of Political Action Committees (PACs), the source of most campaign funding. No matter what its goal or political philosophy, a PAC tends to contribute money to influence those already in power. Why take a chance on a challenger when a $5,000 gift, the maximum one PAC can give a candidate for one campaign, will get an officeholder's attention and maybe his vote? Contemplate this alarming measure of entrenchment: In the 1986 election, over 98% of House incumbents who stood for reelection won. Only about 50 incumbents will have to campaign vigorously, Mann estimates. ''Even that's a stretch,'' he adds. ''Many will have a few sleepless nights but win easily.'' The only sure turnover will be in the 27 seats being vacated. One of the retirees is Peter Rodino of New Jersey, chairman of the Judiciary Committee for the past 15 years. Replacing him will be Jack Brooks of Texas, a populist protege of Lyndon Johnson who, in the admiring words of one student of Congress, is ''meaner than a junkyard dog.'' Should President Bush pursue his quest for the right to strike specific expenditures from appropriations bills -- the line-item veto -- Brooks will lunge. But one business lobbyist thinks that on antitrust legislation Brooks will be easier to work with than Rodino, who automatically equated big with bad. The only other certain change in a major committee will be the succession of Leon Panetta of California to the chairmanship of the Budget Committee. Perhaps because he represents seaside Monterey, Panetta is one of Congress's more genial barons. But he is known for his detailed knowledge of what government departments spend. Dan Rostenkowski will remain as chairman of House Ways and Means, where tax legislation begins, and John Dingell will still rule Energy and Commerce, through which nearly half of all legislation eventually passes. THERE IS an outside chance the Senate will change dramatically. Although a Senator has to face election only every six years, his career is not quite as secure as a House member's. Because Senators have ideas bigger than a congressional district, they attract more attention and therefore arouse more criticism. Democratic consultant Ann Lewis explains: ''Senators have become the ideological point people, and for that reason are more vulnerable.'' Individuals, as distinguished from PACs, are willing to open their wallets wide for a glamorous Senate challenger -- Superman, for example. Republican Pete Dawkins, who in 1958 won the Heisman trophy as a halfback for West Point and was later a Rhodes scholar, one of the Army's youngest generals, and a Shearson Lehman investment banker, has raised over $5 million in his attempt to beat New Jersey Senator Frank Lautenberg, a freshman Democrat. Less than a quarter of the money is believed to come from PACs. Conceivably, a landslide for Vice President Bush could help carry Dawkins and a few other Republicans into the Senate, maybe even enough to overturn the Democrats' 54-to-46 majority. Short of a Bush avalanche, however, the Democrats will likely stay on top and may gain a seat or two. Even under Democratic control the Senate will look a bit different, because of some significant changes in committee chairmanships. Robert Byrd will trade in his majority leadership to take the place of John Stennis as head of the Appropriations Committee, a move that is not necessarily a step down. Appropriations decides where the money ($1 trillion plus) goes. In the 36 years Stennis was on the committee, he helped channel billions to his home state of Mississippi. Says a committee staffer: ''A faucet is going to be turned off that Mississippi didn't even know was on.'' Donald Riegle of Michigan is likely to take over the Banking Committee with William Proxmire's retirement. As a presumptuous young Republican Congressman in the 1960s, Riegle annoyed colleagues by boasting of his presidential plans. In 1973 he decided Republicans were too conservative and switched to the Democratic Party. At 50, Riegle is still a long way from the White House. In the meantime he has assumed a heavy legislative burden. ''I'm the only Senator on all four economic committees,'' he points out. As Banking chairman, he will likely promote his bill to replace the present law's vagueness with a careful definition of insider trading. He also wants to toughen the Williams Act to ensure corporate shareholders of more information prior to tender offers. His first big chore, however, will likely be to help stricken savings and loan associations. SHOULD LLOYD BENTSEN become Vice President, the chairmanship of the Finance Committee will pass, somewhat disconcertingly, to Spark Matsunaga of Hawaii. For decades the crucial committee that writes tax and trade law has been run by such forceful chairmen as Russell Long, Robert Dole, and Bentsen. Matsunaga is a Harvard law school graduate who, like his colleague Daniel Inouye, was a decorated hero of a World War II nisei regiment. But he is unassertive and parochial, spending much of the middle of his day at a Senate dining room table with constituents passing through. The best bet is that authority in Finance will devolve to influential subcommittee chairmen Bill Bradley and Daniel Patrick Moynihan. If the players are basically the same, why should Congress be more truculent? Consider, first, a Bush victory. Says Norman Ornstein, a resident scholar of the American Enterprise Institute: ''The Democrats will be devastated. It will mean 12 consecutive years out of the White House. They will see their role as dominating the agenda through the control of Capitol Hill.'' The Chamber of Commerce, for one, is braced for a preemptive strike by Democrats early next year. The Chamber figures they will probably dare Bush to veto popular programs they haven't been able to push through this year, such as legislation requiring all employers to provide health insurance, day care for workers' children, and a higher minimum wage. What would be more damaging to the country than confrontation, however, would be the opposite: disengagement on the vital issue of reducing the budget deficit. Bush and Congress are on an avoidance course. At last November's economic summit, congressional leaders and President Reagan's deputies agreed to trim the deficit by $30 billion in fiscal 1988 and $46 billion in 1989, which began October 1, with a reduction in spending and some minor revenue enhancement. Congress and the President also created the bipartisan National Economic Commission to come up with a plan for further reductions. HOUSE MAJORITY leader Thomas Foley of Spokane is convinced that deficit reduction will take a combination of cuts in expenditures as well as new revenues. The numbers seem to bear him out. Revenues in fiscal 1990 are expected to fall about $136 billion short of commitments to existing programs. And those revenues could be smaller if Bush, as he has promised in his campaign, gives parents a $1,000 tax credit for day care and cuts capital gains tax rates. New promises the Bush Administration might make, like more ; spending on education, would further widen the gap. Bush nevertheless insists the deficit can be knocked down sufficiently without new taxes (see Letters). All it takes, he says, are spending freezes on just about everything but Social Security, plus economic growth averaging 2.6% a year over four years. Bush's plan rests in part on the optimistic assumption that when the capital markets realize he is serious about reducing the deficit, interest rates and the government's borrowing costs will fall. Congress would most likely ignore a budget proposal from Bush based on a spending freeze. But the lawmakers will not confront him with their own tax plan. In a fine piece of theater when he accepted the presidential nomination, Bush promised that as Congress sent him tax bills, he would turn them down again and again and say finally and emphatically, ''Read my lips.'' But he may never get to deliver the line. Says Foley: ''At the first hint of a veto, a tax bill would have trouble making it out of committee.'' Democrats have no interest in leading a campaign that would be both unpopular and doomed. Assume that Dukakis wins. Even with Democrats in control of both House and Senate, he will be embattled. Ornstein of the American Enterprise Institute makes the case that the Republicans, less enthusiastic about government in general than Democrats, have less stake in making it function smoothly. They have made it work in the 1980s, says Ornstein, partly because the President has been their man. ''With a Democrat in the White House, all restraint will be off. Processes will become slow and tedious.'' Other Republicans might follow the lead of North Carolina's Jesse Helms, who even with Reagan in the White House harassed the State Department. Kevin Phillips, a conservative commentator, believes that Republicans would not be as deferential to Dukakis if he wanted to sign an agreement with the Soviets as they were when Reagan asked their approval of the INF treaty. Republicans will almost certainly have enough Senate seats to block treaties. Dukakis could have difficulty with his own party as well. He too breezily ignores the budgetary consequences of his spending plans. Dukakis will consider taxes only as ''a last resort,'' he promises. He will first try the waters at other resorts, hoping to catch more revenues through tougher IRS enforcement of the tax code, for example. Congressman Panetta raises an eyebrow. ''That's like counting on offshore drilling,'' he says. ''You just never know what's out there.'' Dukakis's position on taxes dismays some members of the Democratic leadership as much as Bush's. But congressional leaders are not going to stand up publicly and tell Dukakis he has to raise taxes. ''I'm not going to take the heat,'' says Rostenkowski. If the new President asks for advice, the Ways and Means chairman will provide a list of options, most likely headed by taxes on energy and a bite on Social Security benefits. Raising income tax rates will be at the bottom. ''I made a covenant with the American people in 1986 that if they would give up their tax shelters, I would protect low rates,'' says the Chicago bear, holding up a big paw. Rostenkowski will give the President no more than his advice and his vote. ''I'm not going to twist any arms in Congress for him,'' he says. ''He has to do that.''

DEMOCRATS would be loath to vote for new taxes if it meant death by ballot in 1990, for even the law of incumbency might not save them. ''A member is not going to walk off a cliff without a line tied around his waist,'' says Panetta. The other end of the rope would have to be wrapped tightly around an agreement by the Republicans to vote for a Dukakis tax plan. But Republicans, many of them convinced that more taxes are unnecessary, would have little reason to back a Dukakis initiative. Other Republicans may agree that it will be difficult to dissolve the deficit without new taxes but are suspicious -- with good reason -- that the Democrats will use the revenues not to reduce the deficit but for additional programs. Says Senator Bob Packwood, ranking Republican on the Finance Committee: ''The only way there can be new taxes is with an ironclad, statutory guarantee that they wouldn't be used for new spending, and I'm not hopeful.'' The National Economic Commission could yet provide a path out of the mess, notably a proposal that would meet Packwood's requirement and shield both parties from solitary blame for a tax increase. Failing that, the rift between the White House and the combative Congress could grow very wide, and the deficit would remain as intractable as ever.