NEW YORK (CNN/Money) - After slashing interest rates to new 40-year lows, there's not much ammo left in Alan Greenspan's gun; but there are a few things he and his compadres at the Federal Reserve could do to try to help the U.S. economy even if all their bullets were gone.

The only question is: Would they work?

"Traditional monetary policy is using open-market operations to affect the fed funds rate, which is the lever," said former Fed Governor Lawrence Meyer, now a visiting scholar at the Center for Strategic and International Studies. "If that lever is pushed all the way down...there are things you can do."

Remember: these are in-case-of-fire-break-glass measures for when the economy is in real trouble -- if you see Fed policy makers performing the following tricks, you can get a pretty good idea of just how desperate they are.

The Fed can push short-term interest rates lower by buying short-term government bonds. By increasing the demand (and price) for these bonds, the Fed's purchases push rates lower, since bond yields move opposite to their price.

In response, banks would turn around and cut their lending rates, encouraging spending and investment.

But when the Fed is out of short-term ammo -- and it's awfully close after last week's rate cut -- it could pump more money into the economy by buying long-term bonds to push those rates lower. Long-term government bonds are a relatively safe investment, and they'd have an impact on other long-range debts, including mortgages -- meaning the refinancing boom would have fuel to continue.

The Fed could also buy corporate bonds to make corporate borrowing cheaper. It could even buy stocks to help support stock prices, making that another attractive way for companies to raise money. It could further diversify into overseas equities, having an impact on exchange rates.

"Anything the central bank buys constitutes an asset and allows it to expand its liability of money supply," said Cornell economics professor Warren Bailey.

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What and how much the Fed can buy is limited by law, but if the economic stew gets hot enough, Congress might be inspired to give the Fed more buying power.

"The basic idea here is that you have to engage in a wider range of asset purchases to carry out open-market operations," former Fed Governor Meyer said.

Many of these assets, especially stocks, could be pretty risky, and watching the Fed take such chances could sound a note of desperation, damaging investor psychology.

Of course, if the Fed is in a situation where it finds itself having to buy stocks -- something the Bank of Japan is considering doing as a way to get out of that country's decade-long recession -- investor psychology would already be pretty far gone.

If the Fed's out of interest-rate ammo, it can at least talk about keeping money supply flowing, which would help keep interest rates low, sort of like the Secretary of the Treasury can cause the value of the dollar to plunge simply by saying publicly that the government doesn't care about supporting it.

"You need to communicate as well as you can that you will hold rates low longer than markets expect; then long-term rates will fall relative to short-term rates," Meyer said.

While merely communicating is a lower-risk tactic, it might be utterly ineffective if the Fed has no credibility -- a very real possibility in an economy in bad enough shape that the Fed's having to take some of the drastic actions listed here.

According to Fed regulations, when you deposit a dollar at your local bank, the bank is free to run out and buy stuff or make loans with most of that dollar, but it has to keep a certain percentage of it on deposit. Cutting that reserve requirement would give banks more money to lend and spend.

But Cornell's Bailey pointed out that all this extra money might mean nothing if banks don't have any qualified loan candidates or if already deeply indebted companies and households have no stomach for more debt.

"When we had the tax cut a while back, [people] put it in the bank," Bailey said. "The Fed can open certain gates, but it can't necessarily force the water to go through."

The Fed also controls the amount of stock investors can buy on credit, or "margin." Some economists have criticized the Fed for not raising margin requirements in the 1990s, saying the speculative stock-buying of low margin requirements helped build a dangerous stock-market bubble.

But if the economy's in a death spiral and interest rates are at zero, a temporary stock-market bubble might not be such a bad thing, and allowing more margin buying could help fuel that.

"As the equity markets react positively to this change, we get a bit of a positive wealth effect which in turn should induce higher consumer spending," said Anthony Chan, chief economist at Banc One Investment Advisors.

Some economists have suggested that, when interest rates and inflation are very low, the Fed can help make spending more attractive by targeting a higher rate of inflation, so that the cost of hanging on to money will be greater than the cost of spending it.

While some have suggested (only half-jokingly) fueling inflation by dumping money out of a helicopter, other ideas -- which really aren't much different than dumping money out of a helicopter -- have reportedly been bounced around by Fed officials and economists, including issuing vouchers for consumer goods and printing currency with a magnetic stripe that makes the money lose value the longer it stays in your wallet.

But these methods aren't guaranteed to raise inflation, and they might smell a wee bit desperate.

"They've really lost their minds [at the Fed] if they really think that's the kind of thing that's going to do anything other than collapse the economy," said Jim Bianco, president and research director of BiancoResearch.com.

In fact, a few economists have even suggested that the Fed has helped create the economy's current problems by making money too easily available. The best thing the Fed could do, they suggest, is raise interest rates.

This would clearly be a radical move, bucking conventional wisdom. But higher interest rates would help financial institutions and other debt-holders, and would also help the people who have money in interest-bearing accounts.

"One thing to understand about interest rates is that they're bad in both directions," Bianco said. "Having rates at an extreme low is bad. By encouraging them to go further, the Fed only makes it worse."

Rates will almost certainly stay low, but it would seem the effectiveness of any possible Fed action, including further rate cuts, will be limited. With rates already at rock-bottom and people in debt to their eyeballs, it seems unlikely that there's enough demand for more debt to make increasing the money supply worthwhile.

"There is no trick to enable the Fed to induce the private sector to want to borrow," said former Fed Governor Andrew Brimmer, president of Brimmer & Co. in Washington. "That's why the burden now switches to fiscal policy."

Which is why Greenspan's most effective trick might be telling Congress, when he addresses the Joint Economic Committee of the House and Senate on Wednesday, to cut taxes.

As for the rest of the Fed tricks, don't expect to see them performed any time soon. The Fed hasn't really tried them before, with a few exceptions here and there during the Great Depression, and most economists say they won't be necessary. They'd better be right.