D.C.mayoral aide Joseph P. Yeldell's defense attorney asked yesterday to withdraw from representing Yeldell in a September bribery trial, and sources said part of the reason is that he is not being paid by his client.

Yeldell and multimillionaire developer Dominic F. Antonell Jr. are scheduled to go to trial Sept. 18 before U.S. District Judge Gerhard A. Gesell on bribery and conspiracy charges regarding the awarding of a city lease to a building owned by Antonelli at 60 Florida Ave. NW.

In asking Gesell to allow him to withdraw, defense attorney Curtis R. Smothers gave no explanation for wanting out of the highly publicized case after representing Yeldell for about 1 1/2 years.

The brief motion field by Smothers only stated that he had advised Yeldell that he should find another attorney, and that Smothers did not believe his withdrawal would postpone the fall trial date.

The withdrawal motion was filed amid reports in the Washington legal community that Yeldell had not been paying his attorney's, Smothers and Smother's former partner, Gary Myers, for some time, and had been unwilling to work out a payment schedule with them.

In one instance, a professional acquaintance told Smothers that some contributions recently had been made to Yeldell legal defense fund. Smothers seemed surprised to hear that, the acquaintance said, and appeared unaware that any such contributions had been made.

Smothers declined to comment on his withdrawal motion. Yeldell did not return a reporter's telephone call.

The withdrawal at this stage of the case - between indictment and trail on serious corruption charges - was seen by some lawyers as posing an unusually serious problem for Yeldell in seeking new attorneys. Smothers, for example, had just received 30,000 pages of documents from prosecutors to begin reviewing in connection with the fraud trial.

Some sources have told The Post that Yeldell's attorneys also have expressed concern over their client's possible lack of candor with them on financial as well as other issues.

Smothers and Myers have represented the former mayoral aside since November 1976, when Yeldell's actions as director of the D.C. Department of Human Resources were called into question. News accounts at the time listed allegations of nepotism, cronyism and leasing abuses by his agency.

Smothers and Myers became Yeldell's lawyers at the height of criticisms against him and by April 1977, had guided him through several city government investigations. Those investigations failed to establish bay wrongdoing by Yeldell, and Mayor Walter E. Washington subsequently named him to be the No. 3 man in his administration.

A federal probe of Yeldell's leasing activities remained very much alive, however, and last month Yeldell and Antonelli were indicted on the bribery and conspiracy charges.

Following the indictment, Mayor Washington and Yeldell agreed that the latter should be placed on leave with pay - paid vacation - while he worked and Antonelli both pleaded innocent, and trial date was set.

Meyers, who handled much of the defense work for Yeldell during the city government investigations, recently left the law firm. Smothers had been preparing to handle the case in federal court.

In the indictment, Yeldell is accused of steering the city to lease Antonelli's building in return for a hidden loan for $33,000 from the parking lot magnate and for other alleged financial favors.