Under prodding from a congressional subcommittee yesterday, Securities and Exchange Commission Chairman John S. R. Shad acknowledged that, if his agency had the power to regulate government securities dealers, it might have minimized the E.S.M. Government Securities fiasco that resulted in the first "bank holiday" since the Depression.

"I do not think self-regulation or direct regulation by the SEC would have prevented the fraud, when so many people were involved, but we could have caught it earlier," Shad said. "The situation would have been a hell of a lot worse if we hadn't intervened on March 4."

The House subcommittee on telecommunications, consumer protection and finance ordered the SEC to tell Congress within 90 days whether it or some other government agency should regulate government securities dealers.

Reps. John D. Dingell (D-Mich.) and Timothy E. Wirth (D-Colo.) accused the SEC of hedging on the issue for the past 14 months. The two legislators made it clear that a series of failures of government securities firms since 1982 has convinced them it is time to crack down on this unregulated industry.

E.S.M., a Fort Lauderdale government securities firm, was placed in receivership March 4 after losses of about $315 million were discovered. The firm is accused of fraud in pledging the same government securities as collateral for several different deals with financial institutions and municipalities. The losses caused the failure of Home State Savings and Loan of Cincinnati, setting off a financial panic that resulted in the closing of all state-chartered savings institutions in Ohio.

The only power the SEC now has over government securities dealers such as E.S.M. is to accuse them of fraud. The SEC tried to go after E.S.M. in 1977 on the grounds that it was setting excessive markups, but did not have the power to pursue the case.

Thirty-six major dealers in government securities come under voluntary capital adequacy standards set by the Federal Reserve. Others are entirely unregulated.

Because monetary policy and the liquidity of the markets are involved, Shad and other SEC commissioners questioned whether the Federal Reserve or the Treasury, rather than the SEC, should regulate the market. They will consult with the other agencies and come up with a recommendation.