As two more congressmen and another labor leader joined a growing arrest list at the South African embassy, U.S. Attorney Joseph E. diGenova -- saying the cases lacked "prosecutive merit" -- dismissed charges yesterday against 11 persons arrested previously at the embassy during demonstrations to protest South Africa's apartheid policy of racial segregation.

Five cases of unlawful entry were dropped, diGenova said, because of "evidentiary problems," a reference to the embassy's decision not to press charges for sit-ins that have occurred at the Massachusetts Avenue complex. Lesser charges of congregating within 500 feet of a foreign embassy were dismissed against six others during the day after federal prosecutors determined, in a case-by-case review, that they were not worthy of prosecution.

The charges dropped included those against D.C. Del. Walter E. Fauntroy and Randall Robinson, executive director of the TransAfrica lobbying group, whose arrests Nov. 21 triggered a Free South Africa Movement that has attracted a growing number of demonstrators outside the embassy.

But even as charges against them, Reps. Charles Hayes (D-Ill.) and Ron Dellums (D-Calif.), Yolanda King, daughter of Martin Luther King Jr., and others were being dropped, a new group of protesters was going to jail.

Arrested yesterday, after they refused to leave the front of the embassy, were Rep. Don Edwards (D-Calif.), the first white congressman to join the demonstrators, Rep. George W. Crockett Jr. (D-Mich.), a member of the Congressional Black Caucus, and Leonard Ball, national coordinator of the Coalition of Black Trade Unionists.

Though diGenova would not elaborate beyond his brief statement dismissing the unlawful entry charges, sources close to the U.S. attorney's office cited several factors behind the dismissals -- and speculated that charges against more defendants, including those arrested in the future, eventually will be dropped also.

There was a feeling among the prosecutors, these sources said, that the embassy charges would only result in "show trials" that would focus attention on the apartheid policies of the South African government but gain little in terms of law enforcement, even in the unlikely event that the District's predominantly black juries returned guilty verdicts.

Given an existing backlog of serious drug and other major crime cases, the Justice Department is not anxious to "clog" the courtroom with defendants arrested in a symbolic, nonviolent protest against racial oppression.

"It's a no-win situation either way you go," said one Justice Department official. "From our point of view, there's nothing to be gained."

One prosecutor further described the cases as dealing with "borderline criminal activity," where "criminal intent to break the law is clear, but the intent to do something wrong clearly is not there."

This prosecutor warned, however, that the Justice Department would take a very different view with demonstrators who are violent or with those who are arrested a second time.

Two of the demonstrators arrested earlier, Rep. John Conyers Jr. (D-Mich.) and William Simons, president of the Washington Teachers Union, were charged under D.C. municipal regulations with entering a police area, which puts their cases in the hands of the D.C. corporation counsel's office. Officials from that office did not return repeated telephone calls yesterday to answer questions about whether those charges, too, would be dismissed.

With yesterday's demonstrators numbering 300, organizers of the protest had to set up two picket lines on both sides of Massachusetts Avenue NW, a block south of the embassy. Police stopped afternoon rush-hour traffic at one point so that more than 60 cameramen, photographers and reporters could watch the arrests from across the street.

Despite the delay, many motorists honked their horns, raised a fist or made other signs of support for the protesters as they drove by the embassy, which is next door to the now-empty Iranian diplomatic mission.

Since Wednesday, the demonstrations and arrests have followed a well-planned pattern, and yesterday was no exception. Protesters arrived at Massachusetts Avenue and 30th Street NW at about 3:30 p.m., set up picket lines and continued their sidewalk march until about 4:15 p.m., when Edwards, Crockett, who is 75, and Ball held a short news conference criticizing apartheid in South Africa and then walked up to the police line set 500 feet away from the embassy.

After telling the police they had an appointment with the the South African ambassador, the three were escorted to the embassy's front door by uniformed Secret Service officers, where they spoke into an intercom, asking to speak with the ambassador. As on previous days, they were told they were not allowed inside without an appointment.

The trio then walked to the sidewalk in front of the embassy, where D.C. police warned them to disperse. Instead, they linked arms and sang a chorus of "We Shall Overcome," the anthem of the civil rights movement of the 1960s. After refusing another order to leave -- and after singing another verse of the song -- D.C. police placed them under arrest, searched and handcuffed them and drove them to 2nd District police headquarters.

Despite the seemingly orchestrated, tactical cooperation with the protesters, police officials say they are only following a common policy of accommodating the wishes of demonstration leaders to maintain order and discipline.

But with D.C. Mayor Marion Barry's public endorsement of the antiapartheid campaign -- he was at the protest site Thursday to offer praise and to discuss the possibility of his own arrest -- there is something different about this demonstration.

"We're trying to walk a thin line and still be law enforcement officials," said one police official privately. "You can understand what's going on here. Here's the mayor standing up saying he may get arrested. He's the chief law enforcement official in the District. You can figure it out."

The protest will take a break over the weekend, when the embassy is closed. On Monday, the anti-apartheid campaign is set to extend beyond Washington to South Africa's 13 consulates around the country.

Gerald McEntee, president of the American Federation of State, County and Municipal Employees, who was arrested at the embassy Thursday, has called on his 1.2 million union members to participate in Monday's demonstrations.

Yesterday's decision to dismiss charges against most of the embassy protesters was made by diGenova's office alone, sources said. It spared probable jury trials for five persons and minor court action for six others.

In addition to Fauntroy, Hayes and Robinson, unlawful entry charges were dropped against Mary Frances Berry, a member of the U.S. Civil Rights Commission, and the Rev. Joseph Lowery, head of the Southern Christian Leadership Conference. The charge is punishable by six months in jail and a $100 fine.

Besides Dellums, King and McEntee, charges of congregating within 500 feet of an embassy were dropped against Mayor Richard Hatcher of Gary, Ind.; D.C. Council member Hilda Mason (Statehood-At Large) and Marc Stepp, vice president of the United Auto Workers. That charge is punishable by 60 days in jail and a $100 fine.

Conyers and Simons still face charges under D.C. regulations of entering a police area, for which the maximum punishment is a $300 fine.

The absence of jury trials won't do much to dim the glare of publicity already generated by the embassy demonstrations and daily arrests.

"Last night was my first time in jail," Yolanda King, the slain civil rights leader's 29-year-old daughter told reporters yesterday, after spending a night in jail. She said the experience heightened her respect for her father's sacrifices.

Gus Williams, the Bullets' leading scorer at 20.9 points per game, leads the NBA in steals with 47. Williams and Dudley Bradley are the only Bullets with more steals than turnovers: Williams, 43 turnovers; Bradley, 29 and 27. Last season, eight NBA players with at least 1,000 minutes had more steals than turnovers: T.R. Dunn, 173-97; Rickey Green, 215-172; Darwin Cook, 164-42; Lester Conner, 162-143; Lafayette Lever, 135-125; Trent Tucker, 63-54; Kyle Macy, 123-116 and Bobby Jones, 107-101.