The opponents of the measure gloomily predicted that by unshackling banks and enabling them to move more freely into new kinds of financial activities, the new law could lead to an economic crisis down the road when the marketplace is no longer growing briskly.

''I think we will look back in 10 years' time and say we should not have done this but we did because we forgot the lessons of the past, and that that which is true in the 1930's is true in 2010,'' said Senator Byron L. Dorgan, Democrat of North Dakota. ''I wasn't around during the 1930's or the debate over Glass-Steagall. But I was here in the early 1980's when it was decided to allow the expansion of savings and loans. We have now decided in the name of modernization to forget the lessons of the past, of safety and of soundness.''

Senator Paul Wellstone, Democrat of Minnesota, said that Congress had ''seemed determined to unlearn the lessons from our past mistakes.''

''Scores of banks failed in the Great Depression as a result of unsound banking practices, and their failure only deepened the crisis,'' Mr. Wellstone said. ''Glass-Steagall was intended to protect our financial system by insulating commercial banking from other forms of risk. It was one of several stabilizers designed to keep a similar tragedy from recurring. Now Congress is about to repeal that economic stabilizer without putting any comparable safeguard in its place.''

Supporters of the legislation rejected those arguments. They responded that historians and economists have concluded that the Glass-Steagall Act was not the correct response to the banking crisis because it was the failure of the Federal Reserve in carrying out monetary policy, not speculation in the stock market, that caused the collapse of 11,000 banks. If anything, the supporters said, the new law will give financial companies the ability to diversify and therefore reduce their risks. The new law, they said, will also give regulators new tools to supervise shaky institutions.

''The concerns that we will have a meltdown like 1929 are dramatically overblown,'' said Senator Bob Kerrey, Democrat of Nebraska.

Others said the legislation was essential for the future leadership of the American banking system.

''If we don't pass this bill, we could find London or Frankfurt or years down the road Shanghai becoming the financial capital of the world,'' said Senator Charles E. Schumer, Democrat of New York. ''There are many reasons for this bill, but first and foremost is to ensure that U.S. financial firms remain competitive.''