The 5 p.m. Soviet press conference was about to begin in an auditorium packed with western and Soviet journalists when a stir began in a middle row.

Cameras and journalists switched their focus away from Soviet Foreign Ministry spokesman Vladimir Lomeiko and zeroed in on a small, pale, gray-haired woman who just three weeks ago left the Soviet Union after receiving a long-sought exit visa.

Apparently because of disruptive episodes involving Irina Grivnina yesterday and this morning, a Swiss security officer asked her to leave the conference. She loudly asked why.

Lomeiko, angry, insisted that she end her "provocation" and told western newsmen to stop paying attention. Soviet journalists yelled, "Out, out." Swiss officials later revoked Grivnina's press credentials.

Lomeiko by then had stormed out of the hall to hold his briefing in a small conference room upstairs. Once again, Soviet efforts to match western-style press briefings were upset by a Soviet dissident.

In the Soviet Union, Grivnina had been a leading member of a group that monitored alleged abuses in psychiatry. She spent one year in prison and 20 months in internal exile before being allowed to leave for the Netherlands.

Accredited here by a Dutch weekly, Grivnina yesterday attended a Soviet press conference on arms control and put the briefers on the spot with questions about political prisoners in the Soviet Union.

When Soviet leader Mikhail Gorbachev arrived this morning at the airport, Grivnina shouted out comments about human rights, asking for the release of Nobel Peace Prize laureate Andrei Sakharov.