In an atmosphere mixing good-humored banter with courtroom drama, the intricate jury selection process began yesterday in the bribery and conspiracy trial of former D.C. mayoral aide Joseph P. Yeldell and wealthy developer Dominic F. Antonelli Jr.

Judge Gerhard A. Gesell, who is presiding at the trial in U.S. District Court here, announced at the end of the day that he hoped to complete the jury selectiona dn allow the government and defense to offer their opening arguments today.

An initial group of 154 jurors was narrowed to 89 after broad-ranging questioning by Judge Gesell in an attemp to assemble an impartial panel. Some were excused because they said they were already familiar with the allegations against Yeldell and Antonelli through news accounts.

Others objected to being sequestered during the trial which is expected to last three to four weeks. The said they had children to care for at night, health problems or other personal difficulties. The jury will be sequestered throughout the trial, probably at a local motel, to avoid exposure to news or other commentary about the proceedings. Still other prospective jurors said they did not believe they could render unbiased verdicts.

Gesell at times underscored the solemnity of the court proceedings, telling prospective jurors of the seriousness of their duties, briefly lecturing one panel member who returned late after a lunch recess and warning all the remaining prospective jurors to avoid reading or listening to any news accounts about the trial during the evening.

Nevertheless, Gesell also established a warm and sometimes off-handed court room atmosphere, sometimes provoking laughter among the tired and occasionally bored group of prospective jurors. "Now ladies and gentlemen," the judge announced at the end of the day, "I have good news and bad news for you.The bad news is that the Yankees are ahead. The good news is that we're through for the day."

Yeldell, the former head of the city's controversy-ridden Department of Human Resources, and Antonelli, a millionaire executive with farflung real estate, parking and other businesses and investments, sat beside one another, often engaged in apparently amiable conversation as the jury selection process continued.

Their courtroom conradelines contrasted with their demeanor last April when they appeared in court to plead innocent to the charges, accusing them of conspiring in the allegedly corrupt award of a $5.6 million, 20-year city government lease for a two-story building at 60 Florida Ave. NE.

In April, they largely appeared to avoid one another's glance and had talked together only briefly during recess.

Yesterday, Antonelli dressed in a conservative black suit and maroon tie and wearing dark-tinted glasses, apparently because of eye ailments, devoted much of his time to poring intently over thick volumes of financial governmental and other records expected to be offered as evidence in the trial.

Yeldell - in a dapper three-piece blue suit, with a red handkerchief in his pocket to match his red and blue striped tie and a gold tie-tack shaped in the letter "Y" - winked at a friend in the courtroom, gazed intently at many of the prospective jurors, doodled on a yellow pad with a red pen and occasionally closed his eyes, in apparent boredom.

Yeldell's wife, Glady's, and several friends including D.C. human rights director James W. Baldwin were in the courtroom.

Neither Antonelli 56, nor Yeldell, 46, nor their principal attorneys - Edward Bennett Williams, who is representing Antonelli, and John A. Shorter Jr., who is defending Yeldell - would comment on the proceedings yesterday.

Among the series of questions Gesell asked the prospective jurors yesterday was one that appeared to cast an ironic light on the public impact of the news media. When Gesell inquired how many prospective jorors had any knowledge of the Antonelli-Yeldell case through newspaper, television or either coverage, about 60 panelists stood up. Then Gesell told them to sit down if they no longer remembered what they had read or heard. Only 21 remained standing.

"That's the way I read the newspapers often myself," the judge remarked amid laughter.

Nonetheless, it was a series of news accounts in The Washington Post nearly two years ago that prompted the federal grand jury investigation that led to Yeldell's and Antonelli's indictments.

The 14-page indictment, returned April 6, accuses Antonelli of secretly giving Yeldell a $33,000 loan in exchange for help in obtaining the lucrative lease for the Florida Avenue building. At the time, Yeldell was DHR's chief, and Antonelli controlled a partnership that owned the building.