During the year's violent demonstrations near the White House, as the visiting shah's eyes filled with tears from police gas, Iranian students in the United States were clearly the vanguard of protest against the Pahlavi regime.

For more than a decade theirs had been the only strong voices of opposition to be heard. But with the uprisings against Shah Mohammed Reza Pahlavi that have racked their country in recent months, they have found themselves suddenly far from the crucial action, watching from distant sidelines as the revolution they have called for over the last 15 years seems suddenly to be beginning without them.

Though crowds of young men and women behind paper masks still march through Washington and other American cities - two large demonstrations are planned for tomorrow - there is a certain sense of irrelevance about such activities.

"With millions of people shouting 'Down with the shah' in the streets of Iran," said one longtime activist in the Iranian Students Association, "it doesn't mean much to shout 'Down with the shah' here in Washington."

Months of violence in Iran have culminated with massive demonstrations throughout the country in recent weeks. Cripping strikes have slowed the vital flow of oil to a relative trickle. The civilian government has been replaced by the military and many of its former officials reportedly arrested as the once seemingly invulnerable regime of the shah struggles to stave off its own demise.

The situation in Iran is now so volatile that many Iranians in the Washington area - not only students but businessmen and professionals as well - have found themselves facing a crisis of conscience.

Mixed with their inevitable worries about families and friends in Iran is the quandary over how they can best help their country: Should they stay in the relative safety of the United States and keep the movement of protest alive here? To the extent that the could undermine vital U.S. support for the shah they think their efforts would be worthwhile, and besides, there are courses to finish and personal problems to resolve.

Or should they risk returning to Iran to support the struggle there? One Iranian scholar visiting the United States put it this way recently: "When we're not in Iran that means we're not committed."

"There are people who want to fight on the front lines and there are people who want to sit at a desk," one protester said recently. "It is a different phase of the struggle."

Some groups, such s the Confederation of Iranian Students, however, have already advised their members that now is the time to return, and a spokesman for the group said that last week that more than 600 of its members in Europe and the United States are already on their way back.

Iranians in the Washington business community, who have generally remained silent about the situation in their home country over the years, are now beginning to speak out against the shah.

Manoucher Parvizian, owner of two oriental rug stores on Wisconsin Avenue, for instance, says he has begun to think seriously of going back to Iran now, though he has spent 19 years raising his family and building his business in the United States.

"Sometimes you keep quiet," Parvizian said Friday, "but now you have to speak . . . You only have one life and you have to proud of what you do."

For years, he said, he hoped for peaceful change, and President Carter's ponouncements on human rights gave him some encouragement. But the situation did not improve in Iran, Parizian said, so now he wants to help the struggle against the shah in any way he can.

Among the estimated 6,000 to 7,000 Iranians in the Washington area, there are certainly those who will support the shah, though they are generally keeping quiet these days. Still others profess not to care anymore.

One owner of a Georgetown boutique, for instance, said his main concern now is to get his uncle out of Iran. Once that's done, whatever happens can happen without him. "The last time I went back there (three years ago), I swore I'd never go back."

But many Iranians and Americans close to the Iranian community remark on the new unity that seems to be appearing as businessmen like Parvizian ally themselves with the basic goals of the student movement: to oust the shah and rid Iran of foreign dominance in its economy, culture and politics.

According to Tom Ricks, an assistant professor at Georgetown University who specializes in Iranian studies, this current unity is an entirely "new wrinkle" in the Iranian-American community.

Though there are only three principal opposition lines in Iran, according to Ricks - the nationalist-Muslim group, the Marxist-Leninists (many of whom are as wary of the Soviets and Chinese as they are of the United States), and the liberal-constitutionalists represented primarily by the National Front - within the United States the various opposition groups are split into as many as 14 separate factions ranging from Trotskyites to Maoists to simple nationalists to theocrats.

One still hears occasional quibbling among the factions, as a spokesman from one group will accuse another of being "willing to compromise with the shah," but no group will say of itself.

Virtually all, as well, profess the hope that once the shah is gone the people of Iran will be able to choose freely whatever form of government they wish.

Though the principal causes for the uprisings in Iran can be traced to fundamental problems in its economy, the distribution of wealth and the shah's reportedly oppressive rule, to some unmeasurable extent the education in the United States of so many Iranian - many of them the future leaders of their country - has also played a role.

"The students are young when they come here. They become adapted to a situation where they can say what they think," said Mohammed Eghtedari, a spokesman for the Confederation of Iranian Students and the proprietor of Asia Books and Periodicals in Adams-Morgan. "Then they go back, and if you are a writer you cannot write anything, if you are a poet you cannot say anything . . ." The injustices of the society are no longer endurable.

Other student leaders, however, deny that they have ever felt any great sense of liberty in the United States. Like a spokesman for one of the Iranian Students Association groups who calls herself Sheila Amini, they say they have been harassed here by the police and threatened by school administrations for their activities.

"Iranian students in the United States certainly have not felt free," said Amini.

In the past there was also enormous fear of SAVAK, the shah's secret police, which reportedly operated and may still operate in the United States. Though there have been reported reforms and a diminution of its powers in Iran, it has never been disbanded.

Many students, such as Mohannad Basharaf who participated in a demonstration at the State Department on Thursday, say that their families have been harassed by SAVAK in Iran, received summonses to the police headquarters, been questioned about the activities of their children abroad, told falsely, in some instances, that their children have been killed, and in other cases been forced into bankruptcy by the government.

Suspicions still linger, and few Iranian students, are willing to talk openly about their lives. But the magnitude of the open uprisings in Iran, combined with the atmosphere of growing consensus in Washington's Iranian communities, has greatly reduced fears of SAVAK.

The masks, which once were seen as a necessity, now are seen by many demonstrators as symbols, and few make any serious effort to disguise their identities before or after they march. They know that if, and when, they return to Iran, they will no longer wear them.