Fifty years ago yesterday, President Franklin D. Roosevelt signed the Banking Act of 1933, commonly known as Glass-Steagall after its sponsors. On Capitol Hill and at the regulatory agencies, parties were held celebrating the historic law that created federal insurance for bank deposits and banning banks from underwriting securities.

Yet hard by the party suites were hearing rooms where the words were not so sweet. "There is very little left of Glass-Steagall in the marketplace," Securities and Exchange Commissioner Bevis Longstreth told the House Energy and Commerce Committee, referring to the escalating entry of banks into the securities business. "Today it is a question of whether to dismantle Glass-Steagall or restore it."

Longstreth, like his boss, SEC Commissioner John S. R. Shad, believes that the public would benefit from the competition generated by banks in the securities business. They insist, however, that banks be governed by the same regulations as brokerage houses.

On the other side of Capitol Hill, David Silver, president of the Investment Company Institute representing mutual funds, argued for the preservation of Glass-Steagall. He objected to an administration proposal allowing banks to underwrite securities through subsidiaries.

"It was the securities affiliates which dragged down the nation's largest banks in the debacle of the 1920s," Silver reminded the Senate Banking Committee.

Robert E. Linton, chairman of Drexel Burnham Lambert and the Securities Industry Association, opted for a moratorium that is "an effective two-way plugging of all real or imagined loopholes." He blamed Congress for allowing federal bank regulators to tear down the law.

The biggest loophole of all is that which the Federal Deposit Insurance Corp. proposes to open for federally insured state chartered banks. Because such institutions were not envisioned by Glass-Steagall, they were not mentioned in their act. Therefore FDIC Chairman William Isaac has proposed to allow these 9,000 banks to underwrite corporate securities, subject to some limitations.

This most serious challenge to Glass-Steagall will be the subject of an all-day hearing today at the FDIC.