The Secret Service said yesterday that it is investigating an incident in which an agent reportedly shoved Condoleezza Rice, a Soviet affairs specialist and one of the Bush administration's top ranking blacks, as she was waiting in a line of dignitaries to say goodbye to Soviet leader Mikhail S. Gorbachev.

Other staff members "came to the rescue" and intervened so she could return to her place in the farewell line at San Francisco International Airport Monday evening, a White House official said.

White House Press Secretary Marlin Fitzwater said President Bush is "very upset about it. It's most unfortunate. It should not have happened, and the Secret Service will take appropriate measures."

Asked whether Rice's race was a factor in the attempt to shove her out of the receiving line, Fitzwater replied, "We have no idea what the factors were."

Rice, 35, a professor of political science at Stanford University before joining the White House staff last year, was not talking to reporters about the incident, White House officials said.

As a director of European and Soviet affairs at the National Security Council, she had been deeply involved in preparations for last week's summit conference between Bush and Gorbachev. She flew to Minneapolis and then to San Francisco aboard a U.S. Air Force jet carrying officials responsible for coordinating Gorbachev's cross-country tour.

Fitzwater refused to give details of the incident, other than to tell reporters, "a Secret Service agent pushed Condi Rice. It's as simple as that. You've all had it happen to you 100 times."

Rice was wearing a White House identification pin at the time and was said to have identified herself as a staff member.

Secret Service spokesman Bob Snow said the incident involved an agent from a field office rather than from the traveling protective detail.