Joseph P. Yeldell, a top aide to D.C. Mayor Walter E. Washington, and Dominic F. Antonelli Jr., a millionaire real estate developer, were convicted yesterday on charges that the powerful city official had corruptly traded a D.C. government lease for a secret $33,000 personal loan from the influential businessman.

The federal jury's verdict, reached with stunning swiftness, was announced at midafternoon in a tense courtroom after a three-week U.S. District Court trial.

Yeldell, 46, and Antonelli, 56, maintained impassive expressions as the guilty findings were read, but Yeldell's wife, Gladys, who was seated in the courtroom audience, burst into tears. The jurors had taken only about 3 hours and 40 minutes to convict the two men on the bribery and conspiracy counts with which they had been charged.

After the verdict was announced, Yeldell, who is on unpaid leave from his city government job, quickly left the defense table to comfort his wife and his younger daughter, Joi Lynn, 16, who was also in the audience. They were surrounded by a group of friends, including some D.C. government officials, who paced back and forth along a courthouse hallway, talking sadly among themselves. Lillian Manson, Yeldell's personal secretary, rushed from the courtroom, saying, "Dirty bastards." Yeldell made no public statement.

Yeldell's lawyer, John A. Shorter Jr., described the former city human resources director was angry."I'm certain there's going to be an appeal. We're just not talking at this moment," Shorter added, a few minutes later.

Antonelli, a publicity-shy, gray-haired developer and parking company owner who wears tinted glasses because of eye ailments, strode from the courtroom to make a telephone call from a pay phone in the courthouse hallway. Then he left the building. His chief defense lawyer, Edward Bennett Williams, also departed quickly without commenting on the trial.

Earl J. Silbert, the U.S. attorney for the District of Columbia, held a brief news conference later outside the U.S. Courthouse to characterize the guilty verdicts as a renewed message to public officials from D.C. citizens. He described the message as: "Don't cheat us, don't defraud us, don't betray us, don't abuse your public trust."

The three prosecutors on Silbert's staff who had prosecuted Yeldell and Antonelli - assistant U.S. attorneys Richard L. Beizer, Henry F. Schuelke III and Michael Lehr - celebrated their victory privately with their colleagues in the U.S. attorney's office. They did not comment on the verdict publicly.

Judge Gerhard A. Gesell, who presided at the trial, scheduled sentencing for Nov. 30. Both Yeldell and Antonelli were convicted on a single conspiracy count, which carries a maximum sentence of five year's imprisonment and a $10,000 fine.

In addition, Yeldell and Antonelli were each convicted on one bribery count - Antonelli of giving a bribe and Yeldell of receiving it. The bribery charge provides for a maximum 15-year prison sentence and additional fines. The maximum fine for bribery is described in federal criminal law as either $20,000 or three times the amount of the bribe, whichever is greater. In this case, the maximum fine for bribery presumably be $99,000 - three times the secret $33,000 - although this interpretation may be subject to legal dispute.

Mayor Washington was described by a spokeswoman as recuperating from oral surgery yesterday, and issued no statement on Yeldell's conviction. George R. Harrod, the city personnel director, said that Yeldell would continue on unpaid leave until his sentencing. Then, Harrod said, the city's personnel regulations give the mayor the option of taking various actions, including dismissal.

Yeldell's and Antonell's convictions yesterday were the outgrowth of bitter controversy that grew into the biggest political scandal to mark the District of Columbia's nearly four-year-old home-rule government. The controversy-prompted, in part, by disclosures by The Washington Post nearly two years ago about Yeldell's dealings with Antonelli - engulfed Mayor Washington's government for many months. The allegations against Yeldell and Antonelli were recently cited by some of the mayor's political supporters as a key factor in Washington's narrow defeat in last month's Democratic primary in his bid for reelection.

The controversy followed Yeldell's frequently stormy, more than five year tenure as head of the mammoth D.C. Department of Human Resources, the city's sprawling health and social services agency. As DHR director, Yeldell had repeatedly been accused of malpractices ranging from nepotism and cronyism to mismanagement. His agency was often embattled in court suits brought by its critics.

Some of The Washington Post's disclosures in 1976 centered on a drab, two-story office building at 60 Florida Ave. NE - a site that eventually became the focus of the criminal proceedings that led to Yeldell's and Antonelli's convictions yesterday. The building had been leased by DHR, the agency Yeldell headed at the time, from a partnership controlled by Antonelli.

The jury found Yeldell and Antonelli guilty yesterday of corruptly conspiring in 1975 and 1976 to arrange the highly profitable DHR lease from Antonelli's partnership. Under the lease, the District government had agreed to pay Antonelli's partnership $5.6 million in rent over 20 years. Antonellis partnership had purchased the building - along with six other nearby land tracts - for a total of $800,000 at about the same time it concluded the lease with the city.

In exchange for Yeldell's help in securing the city government lease, Antonelli was found guilty of secretly giving Yeldell the $33,000 loan after helping him to obtain a series of short-term loans from Madison National Bank, in which Antonelli is a major stockholder, director and executive committee member. The origin of the $33,000 was concealed in public records by listing it in the name of a "straw," a fictitious person.