Mayor Marion Barry invited himself onto the stage with Nelson Mandela at a sold-out rally Tuesday at the Washington Convention Center, astonishing some officials of the South African leader's U.S. tour, organizers said.

"Barry pushed his way up, right onto the dais," said Christine Dolan, a press secretary for Mandela's national tour. "He and his entourage were on the heels of Mandela."

Dolan said the mayor so disrupted security plans at a pre-rally reception that contributors to a $1,000-a-couple fund-raiser were not allowed to shake hands as planned with the deputy president of the African National Congress.

Barry's press secretary, Lurma Rackley, said yesterday that she was certain the mayor did not disrupt the reception. She said the mayor had "a kind of a standing invitation" to the Tuesday night reception and rally.

On the printed program for the Tuesday night rally, the mayor's wife, Effi, was scheduled to present the key to the city to Mandela and officially represent the District. More than two weeks before, Mandela's tour organizers said they had received a letter from the mayor explaining that he would be unable to meet with Mandela because of Barry's drug and perjury trial.

Tour organizers said they were dismayed to learn that Barry's plans changed Monday night when Barry told WJLA-TV (Channel 7) news that he planned to welcome the South African leader at the Tuesday night rally, where he sat on the stage behind Mandela.

"He had this sense of where he was supposed to sit and walked in. We were all left kind of with our mouths open . . . . Mandela is not supposed to be entangled with these tawdry, local controversies," said a tour organizer who asked not to be identified.

Barry arrived with about 10 aides at the pre-rally reception, which was attended by several hundred people and sponsored by the Mandela D.C. Welcoming Committee in the lower lobby of the Convention Center, Mandela tour organizers said.

According to Dolan, Barry and his entourage did not follow the protocol set by State Department security officials. If they had, all the guests would have been allowed to file by Mandela in an orderly fashion to shake his hand.

Near the end of his address, Mandela apologized to the contributors for having not been able to greet them personally.

"It got to be a little bit of a mob scene," Dolan said. "Barry was right on his {Mandela's} heels. The State Department said 'forget it.' "

Before the rally, the mayor, accompanied by his wife, met with Nelson and Winnie Mandela in a holding room where others also were present. The mayor presented a key to the city to the African leader off stage because the rally was running behind schedule, Barry's press secretary said.

According to a Mandela national tour organizer, the mayor "had to find somebody who had the key to the city. Mr. and Mrs. Mandela didn't say anything. They looked embarrassed. It was a very awkward situation. It was stressful for everyone concerned."

The mayor changed his mind about not attending the Tuesday night activities after deciding that his appearance would not detract from Mandela's three-day visit, his press secretary said. The mayor received a sustained minutes-long ovation from the audience in the Convention Center in a rally that became a cheering farewell to Mandela.

Barry's appearance on stage was not the only rough spot during Mandela's time in Washington. Two men who were among 25 demonstrators protesting to show support for the white minority government in South Africa were arrested Sunday afternoon in front of the country's embassy. They were charged with assault on a police officer.

Staff writers Veronica T. Jennings and Sharon Epperson contributed to this report.