Iranians supporting the main group fighting the government of the Ayatollah Ruhollah Khomeini marched through downtown Washington yesterday, shouting their opposition to arms sales to Khomeini.

About 1,700 Iranians, a large number from outside the Washington area, chanted slogans in support of the People's Mojahedin of Iran, and its leader, Massoud Rajavi. The organization, which sponsors political protests and attacks on government installations in Iran, announced the formation of a conventional-style army to try to topple the Khomeini government.

A column of demonstrators streamed from the Ellipse to Dupont Circle and back, waving flags and posters of Rajavi and his wife. They shouted back slogans chanted by organizers through loudspeakers.

Camera crews along the route and in a helicopter overhead filmed the march for the People's Mojahedin, which plans to beam television pictures of the rally back into Iran.

Many of the marchers were professionals and students who came from Iran to the United States during the fight against Shah Mohammed Reza Pahlavi or after the Islamic revolution led by Khomeini. There were also about 25 former Iranian military officers in uniform, a number of Americans and Europeans married to Iranians, and families with children or babies in strollers.

"We want Americans to know how much we oppose Khomeini, that we want to overthrow him because of his suppression and killing of our people," a young woman shouted over the din of chanting. She said she was a student at Santa Monica College in California, but declined to give her name because "in Iran, the government will attack our families if they know who we are."

The People's Mojahedin was founded in 1965, joined with Khomeini's forces in opposing the shah, but split with the ayatollah in 1981. Since then, the group has sent guerrilla-style forces into Iran from neighboring Iraq to attack government civil and military installations. State Department officials, including Assistant Secretary of State Richard Murphy, have periodically described the group as "terrorist," but have never moved to limit its organizing efforts in the United States. The group says it is conducting a legitimate fight against Khomeini that consciously avoids hurting innocent Iranians.

The group, which has claimed a sharp intensification of its military fight since the beginning of the year, announced the formation of a National Liberation Army of Iran. Spokesman Shahin Gobadi said the army will "shatter Khomeini's military apparatus and enhance the public uprising we are working for" to overthrow the Tehran regime.