Those programs allow about 15 percent of their collateral to be in equities or debt that is below investment-grade, and most of that is reserved for equities.

On Friday, Timothy F. Geithner, president of the New York Federal Reserve Bank, urged Wall Street chieftains to come up with a solution to stem the growing crisis of confidence. Echoing comments made earlier in the week by the Treasury secretary, Henry M. Paulson Jr., Mr. Geithner said the government would not rescue financial firms.

In the end, the government succeeded in getting Wall Street to create its own insurance policy. But at the same time, the Fed, in agreeing to loosen terms under which it lends money to firms, is potentially putting more taxpayer money at risk.

The events over a harrowing weekend indicate that top officials at the Federal Reserve and at the Treasury will take a harder line on providing government support to troubled institutions. But that does not mean they are unwilling to provide indirect help, or even relax regulatory requirements temporarily.

At first glance, the new strategy by Mr. Paulson and the chairman of the Federal Reserve, Ben S. Bernanke, represents a purer and tougher insistence that Wall Street work out its own problems without government help.

But before the weekend was over, it was also clear that they could stand by their principles  and be creative, too. For example, if Bank of America completes its acquisition of Merrill Lynch, its capital reserves would immediately fall below the minimum requirements for bank holding companies. Regulators, including the Federal Reserve, would have to show lenience for as long as it takes the capital markets to regain their confidence  which could be quite a while.

And the expansion of the Fed’s lending facilities adds another novel approach to help stabilize markets, but without supporting yet another bailout.