The Federal Reserve Board yesterday formally opposed legislation that would force detailed disclosure of policymaking sessions of its Federal Open Market Committed and 12 regional Federal Reserve banks.

Arthur F. Burns, the board's chairman, said the measures would have "a stifling effect upon deliberations" and would risk revealing information about a run on a financial institution in trouble.

Instead, Burns asked a House Banking subcommittee to push to exempt the Federal Reserve from the public disclosure requirements of the Freedom of Information Act on grounds that its operations are super-sentitive.

"Nowadays, there appears to be great currency to the notion that public confidence in our government will be enhanced . . . by exposing to public scrutiny nearly every detail . . . We do not share this view," Burns said.

The measures Burns opposed include two separate pieces of legislation.

One, a bill by Rep. Mark W. Hannaford (D-Calif.), would require the policymaking Federal Open Market Committee to maintain detailed minutes of its meetings and make them public in three years.

The other, by Rep. John J. Cavanaugh (D-Neb.), would require directors of the Fed's 12 regional banks to keep verbatim transcripts of each of their meetings and submit them uncensored to key congressional committees.

The Hannaford bill would reserve a 1976 decision by the FOMC to stop keeping lengthy minutes containing the views of individual members of the panel. The Fed had been releasing the documents at the end of five years.

The switch occurred after the Fed became the target of a suit under the Freedom of Information Act. A federal court ruled recently that FOMC minutes must be made public promptly. Burns said the Fed plans an appeal.

Burns indicated during the hearing that he is working out a compromise with Hannaford on the FOMC legislation. But he flatly opposed the Cavanaugh bill as likely to upset operations of the regional Federal Reserve Banks.