Two separate groups of American radicals marched through downtown Washington yesterday, demanding the return of deposed shah Mohammad Reza Pahlavi to Iran and accusing the United States of precipitating war in the Middle East.

About 300 members and supporters of the Progressive Labor Party, a small but militant communist organization, marched from Meridian Hill Park to McPherson Square chanting, "Death, death, death to the shah," and "Make war on the bosses, not on Iranian workers."

At the same time, a colorful assortment of about 75 protesters from the Socialist Workers Party, Yippies, Revolutionary Students Brigade and the D.C. Area Feminist Alliance marched from Farragut Square to Gallery Place Mall, shouting, "The shah must face the people's wrath. We demand you send him back."

The current drumfire of Iranian-related demonstrations here thus continued unabated, though the two protesters yesterday drew a few of the hecklers and counterdemonstrators that dogged earlier protests by Iranian Moslem students.

Only a few individuals shouted catcalls and obscenities at the marchers yesterday -- a fact that police attributed to the relative quiet of weekends downtown.

Also, since most of the demonstrators were American -- not Iranian -- , many bystanders appeared unsure which side of the Iranian issue the protesters were on. Most stared passively as the marchers went by.

The two separate marches occurred smoothly -- with one exception. About 25 protesters at the head of the Progressive Labor Party march suddenly broke ranks at 15th and G streets NW and began running toward the White House a block away to the west, instead of continuing north on 15th Street as required by police.

Officers, their batons drawn, quickly intercepted the group and herded them back into the line of march. There were no arrests.

Despite the relative smallness of the two demonstration groups, both D.C.

and U.S. Park police turned out in large numbers. The Carter administration, as part of its policy of caution and restraint in the tense Iranian hostage situation, has told Mayor Marion Barry and National Park Service authorities to take all precautions to minimize violent clashes between pro and anti-Iranian demonstrators.

Police have also generally followed Carter administration policy of curtailing demonstrations in Lafayette Square or other places near the White House.

Administration officials say they don't want demonstration pictures broadcast to Iran to suggest that the White House -- symblic heart of the nation -- is under siege.

At a Progressive Labor Party rally in McPherson Square, party member Mike Golash told the cheering crowd "Working people are not going to be suckered in by the people in the White House and Wall Street . . . Their days are numbered."

While calling for the shah's return to Iran, Golash said this did not mean they support Ayatollah Ruhollah Khomeini and his Revolutionary Council.

"Khomeini is like a Rockefeller only a small potato," he said. "They're all part of the same game plan."

He said the plan was to pave the way for a U.S. military move to take control of Iran's oil.