U.S. District Judge Howard F. Corcoran, a member of the federal bench here for the past 12 years, said yesterday that he will step down from fulltime duty Nov. 30.

The decision by Corcoran, who is 71, to take "senior" judge status clears the way for President Carter to make the second nomination of his administration to the 15-member federal trial bench here. Corcoran will continue to draw his full salary while serving in senior status, and said he plans to render "substantial" judicial services although vacating his full-time judicial role.

During his years on the bench, Corcoran has been involved in many high-visibility cases.

He once issued an order temporarily blocking the House Un-American Activities Committee from beginning a hearing on campus unrest, set aside a D.C. rule requiring welfare recipients to allow investigators into their homes, and ruled that the D.C. government could not enforce a one-year residency requirement for new voters.

In criminal cases, he presided over a lengthy police bribery trial growing out of Robert Earl Barnes housebreaking investigation and presided over the trial of a man who held the Philippines ambassador hostage here for several hours. Corcoran recently received criticism, however, for what prosecutors felt were too-lenient sentences in white-collar cases.

Corcoran is a native of Rhode Island, and practiced law in both New York and Washington before being nominated to the bench by former President Johnson. He is the brother of prominent "New Deal" lawyer Thomas (Tommy the Cork) Corcoran.