More than 1,000 Iranians staged a peaceful demonstration against the regime of the Ayatollah Khomeini in Lafayette Square yesterday, as similar protests were scheduled to occur in 17 European and Asian cities.

The protest was organized by the Moslem Iranian Students Society, which said it was the largest the group has sponsored in North America.

"We are here to support the resistance against the Khomeini regime and to honor the memory of the Iranians who were killed on this day four years ago," said Ali Safavi of Alexandria, an organizer of the protest, which drew Iranians from as far away as Miami, Los Angeles and Toronto.

Safavi's organization and other supporters of Massoud Rajavi, a leader of Iran's resistance movement who is exiled in Paris, recognize June 20 as the "Day of Martyrs and Political Prisoners." On June 20, 1981, nearly 500,000 people gathered in Tehran for an anti-Khomeini demonstration. "That was the last mass demonstration in that city against the Khomeini regime," said Safavi, "because many were arrested and executed."

Yesterday's demonstration here was set to begin at 10 a.m., but some protesters arrived hours earlier to erect stage props and a backdrop painted to depict Iran's Evin prison. It became part of a live act that symbolized the execution of the 50,000 "martyrs" allegedly killed by Khomeini in that country since 1981.

Dressed in green military uniforms and black-and-white striped prison clothing, Iranian students enacted executions of political prisoners in Iran to recorded music and sound effects. Many in the crowd wept at the depiction of a woman with a child being brought to witness the torture of her husband.

"Many people here are crying," said Reza Dashti, a demonstration organizer, "because they know this is the real situation in Iran."

During an orderly march following the demonstration, the group's numbers swelled to 1,800, according to District police. Organizers estimated the number at more than 3,000.

"I feel sympathy for my people in Iran," said a demonstrator. "If we don't topple down Khomeini's regime now, our next generation will have to do it.