(FORTUNE Magazine) – The trade winds are blowing in Washington, and the air is full of inscrutable phrases: Most-favored-nation status. Fast track. Negotiating authority. The ghosts of Reed Smoot and Willis Hawley. But the spring winds are also carrying some of the year's biggest storms on Capitol Hill. At stake isn't only America's trade relationship with China, or China's place in the international trading system, or even a broad free-trade agreement in the Western Hemisphere. At stake also is an immutable law of Washington, seldom recognized, never breached: In the end the Congress does the right thing. Or at least the internationalist thing.

Every time the trade issue rears its head, a pattern repeats itself. The capital girds for an agonizing battle. The insurgents cite American jobs, cheap labor abroad, environmental threats. The free-traders fly to the defensive, citing the virtues of open markets. The vote looks too close to call. The lobbying is furious, the claims on both sides spurious.

And ultimately, the free-traders always win.

Now the cycle has begun again, but this time the Establishment--always internationalist, always free-trade, always bipartisan, always endangered--is really under siege. The threat comes in phases, first on the extension of most-favored-nation status for China, then on giving the White House so-called "fast track" authority to negotiate a free-trade agreement with Chile, finally a vote on whether to admit China into the World Trade Organization, which helps countries set and enforce trade rules. "In the end there is still an internationalist bent," says Republican Representative Jim Kolbe of Arizona, "but it's getting closer and tougher."

It's getting tougher because the objections to trade agreements now are coming from both the right (lock-and-load Republicans, led by Patrick J. Buchanan, the serial presidential candidate) and the left (labor-oriented Democrats, led by Representative Richard A. Gephardt, the likely challenger of Al Gore in 2000). The free-traders' case for extending full trading rights to China has been complicated by concern over the transition in Hong Kong; fears about Chinese influence in American politics as a result of Donorgate; continued doubts about Beijing's dismal human rights record; and worries about the U.S. trade imbalance with China--$40 billion a year and growing.

The effort to extend free trade beyond NAFTA (Chile next, then maybe all of South America) faces the very same hurdles NAFTA confronted four years ago, when Clinton prevailed by mobilizing Republicans and a critical handful of Democrats. Administration officials, worried that Canada already has a free-trade agreement with Chile and that the European bloc is eyeing similar accords with Mexico and a number of South American nations, are asking for special authority to begin their own negotiations. But they enter the battle without three important Democratic allies who bailed them out on NAFTA--former House Speaker Thomas Foley and two Ways and Means heavyweights: Dan Rostenkowski and Sam Gibbons. One top trade negotiator tells me he expects "more than a few sleepless nights."

The free-traders do have six decades of history behind them. The turning point was the 1930 Smoot-Hawley tariff. The special interests descended on Washington to help produce a protectionist trade bill that probably prolonged and deepened the Great Depression. Four years later, in 1934, a chastened Congress delegated most trade policy to the executive branch, and since then a slender majority of congressional free-traders and internationalist presidents has prevailed. "Congress has gone to the brink and never screwed up," says Susan C. Schwab, a former assistant Commerce Secretary who now is dean of the School of Public Affairs at the University of Maryland. "Congress depends on the President to keep it from responding to every protectionist impulse."

In recent weeks White House officials have been worrying about President Clinton's resolve. But he returned from his trip to Mexico reenergized and recommitted. About a fifth of the House has been to China since last November's election. "There's been an erosion," says Representative Robert Matsui of California, the Democrats' point man on the drive for the trade measures, "but not enough to kill these things." Sounds like the same old story, and most likely the same old result.

DAVID SHRIBMAN is Washington bureau chief for the Boston Globe and a Pulitzer Prize-winning political reporter.