In a crowded federal courtroom, an eminent, white-haired judge will open the trial this morning of two men who have already left their imprint on the District of Columbia - outspoken former mayoral aide Joseph P. Yeldell and reclusive millionaire developer Dominic F. Antonelli Jr.

Yeldell, 46, who previously headed the mammoth, controversy-ridden D.C. Department of Human Resources, and Antonelli, 58, who presides over an immense parking, real estate and financil empire, will prepare to face bribery and conspiracy charges. Seated beside them will be two top-flight defense lawyers, Edward Bennett Williams, a national legal celebrity, and John A. Shorter Jr., who is highly regarded in Washington's legal circles.

The charges, which stems from the allegedly corrupt award of a city government lease for a drab, two-story building, grew into the biggest political scandal to mark the city's nearly 4-year-old home rule government.

For many months, the frequently bitter controversy that led to Yeldell's and Antonelli's indictments engulfed Mayor Walter E. Washington's administration. Some of the mayor's own supporters now cite the criminal allegations against Yeldell as a key factor in Washington's narrow defeat in his reelection bid the last month's Democratic primary.

In simplest terms, the U.S. District Court trial will center on an allegedly illegal deal between two of the city's most prominent figures-men who emerged from impoverished back-grounds to positions of considerable stature in separate spheres of city life. Antonelli is accused of secretly giving Yeldell a $33,000 loan in exchange for a lucrative, 20-year, $5.6 million [WORD ILLEGIBLE] for the building at [WORD ILLEGIBLE] Florida Ave. NE.

Both men pleaded innocent to the charges last April.

Lists of possible witnesses, which include the mayor and city administrator Julian R. Dugass, resemble a who's who of the District government also contain names of a number of Washington's business leaders. It is unclear, however, whether the mayor, Dugas or other prominent persons named in the lists will actually be called to testify.

The trial may provide a showcase for Washington's legal talent. Judge Gerhard A. Gesell, who will preside at the trial, is regarded as among the most skilled and perspicacious jurists on the federal bench here. Williams, who is representing Antonelli, and Shorter, who will defend Yeldell, will match wits against a young, aggressive prosecution team, including assistant U.S. attorneys Richard L. Beizer, Henry F. Schuelle III and Michael Leir.

Yeldell, Antonelli and their lawyers have remained unavailable for comment during the past few days. But some persons who have spoken with them recently say both men appear relatively confident and relaxed as they face the start of their trial, although they suffered some initial despondency immediately after their indictments were returned April 6.

"He's been the same Joe Yeldell," one of Yeldell's friends said last week. "He continues to have an off-hand, breezy approach that has been his trademark," said another of Yeldell's colleagues, although noting that Yeldell has previously gone through what he described as a "lot of understandable ups and downs."

Antonelli "seemed to be pretty depressed when the whole thing started," an acquaintance remarked last week, but now he appears to be "feeling pretty comfortable . . . He says he'd like to get it over with."

The costs of the trial as well as the eventual verdicts appear likely to affect the two men in ways as different as the circles in which they travel - one of them being a political figure who is thought likely to want to return someday to public office, the other a private businessman who is believed to have amassed a personal fortune estimated at $30 million.

Yeldell, who has been on unpaid leave from his most recent city government job as a mayoral aide since Aug. 28, is relying on a legal defense fund to pay trial costs. One of his previous defense attorneys, Curtis R. Smothers, withdrew in May amid reports that Yeldell had not been paying his lawyers for some time. William J. Wright, a member of Yeldell's legal defense committee, said last week that somewhat more than $10,000 has been raised so far-an amount that seems considerably less than the cost of such trial.

A scrappy, streetwise youngster who grew up in several of the city's low-income, racially segregated neighborhoods, Yeldell rose to local prominence through a succession of city government positions and a close political alliance with Mayor Washington.

He was named a member of the presidentially appointed City Council in 1967 the first such District legislature of modern times. Later, the mayor chose him to head DHR, the city's largest agency. Yeldell's frequently stormy, more than five-year tenure as chief of the city's main health and social service agency ended amid a widening controversy. Nevertheless, the mayor shifted him to a $47,500-a-year job as his No. 2 adviser. After his indictment, Yeldell went on leave.

Antonelli, who was born in Oklahoma and came to Washington as a youngster, grew up in what one of his friends, has described as a "rathole," on DeSales Street NW, where his corporate headquarters now stands. He once worked as an attendant at a parking lot there.

Today Antonelli, who has pursued the classic American success story of a self-made man, owns an interest in more than $100 million worth of real estate in the Washington area, including the Mayflower Hotel, and controls Parking Management Inc., the city's largest parking firm with over 100 lots and garages bearing the PMI logs. He helped found Madison National Bank, in which he has remained a major stockholder and executive committee member.

Although Judge Gesell initially considered starting the Antonelli-Yeldell trial in June - a period that would have coincided with the D.C. mayoral primary campaign - it was eventually set for today mainly because of requests from Antonell' lawyer, Williams.

Even so, some of the Mayor Washington's political backers regard the trial and surrounding controversy as a cause of the mayor's primary defeat, partly because it prevented Yeldell, a shrewd political strategist, from playing a visible role in the campaign and partly because, they contend, the allegations themselves cost Washington votes, especially in Northwest Washington's predominantly white Ward 3.

"I think that had a lot to do with it," Warren Graves, coordinator of field operations for the Washington reelection campaign, said last month as he talked about the mayor's defeat.

No other political scandal has stired such a furor in the District's brief home-rule era, nor has any reached so high among the mayor's circle of friends.

William C. McKinney resigned in 1976 as the city's environmental services director during a federal investigation of his dealings with private firms that did business with his agency. McKinney, however, was not so close to the mayor as is Yeldell, and the investigation was eventually dropped without returning an indictment. Maj. Gen. Frederick E. Davison withdrew from his appointment as a top city administrator in December, 1974, shortly before the start of home rule, in a controversy over unpaid D.C. incomes taxes.

The Antonelli-Yedell trial will begin with selection of a jury, expected to take a day or more. Because of widespread publicity that has surrounded the trial, the jury is to be sequestered at a local motel, where it will be shielded from news accounts of the trial. An unusually large number of propectives jurors-about 150-has been summoned because of anticipated difficulties is selecting the 12 members and six alternates. The trial is expected to last about three weeks.

It has been nearly two years since The Washington Post first disclosed details of DHR's leasing of the Antonelli-owned building that led to an 18-month grand jury investigation and Yeldell's and Antonelli's indictments. Yeldell has consistently denied any wrongdoing, saying that he did not personally take part in lease negotiations with Antonelli. Antonelli has avoided any comment.