Former D.C. mayor Walter E. Washington testified briefly as a prosecution witness here today at the bribery and conspiracy trial of Joseph P. Yeldell, his one-time closest aide, and Dominic F. Antonelli.

Washington now a lawyer in private practice, said he gave final approval in June 1976 for a $5.6 million, 20-year D.C. government lease Yeldell arranged for a property at 60 Florida Ave. NE controlled by Antonelli.

Washington was asked whether Yeldell a former head of the Department of Human Resources had ever told him before the lease was signed of any financial relationship Yeldell may have had with Antonelli. Washington replied, "No."

The question appeared to bear on the fact that Antonelli had given Yeldell a $33,000 loan just after all obstacles to the lease had been removed. Prosecutors contend the loan was a bribe in return for the lease. Defense lawyers say the loan and lease were unrelated.

The conviction of Yeldell and Antonelli on bribery and conspiracy charges last year was overturned when it was disclosed that a juror had failed to reveal information that might have disqualified her. The retrial was moved here because of publicity in Washington about the first trial.