Canada has asked the State Department to reverse the Justice Department's decision to label three Canadian films as "political propaganda," while a storm of protest boiled up on Capitol Hill yesterday and the American Civil Liberties Union announced plans to challenge the decision in court.

Canadian Embassy officials said that they had requested a "clarification" and, if possible, a reversal of the Justice Department's decision to require a disclaimer on two films about acid rain and a nuclear war documentary produced by the National Film Board of Canada.

The decision, reaffirmed yesterday by Justice, also requires distributors to send the government a list of organizations that have asked to see the films.

On Thursday, a Justice Department spokesman said the action was "not unique," although he said he'd never heard of its being taken before. However, last night another department spokesman said that the requirement has been invoked previously, and he cited three examples from last year, including another acid rain film produced in Canada, "Crisis in Rain," and a West German film promoting business opportunities in Berlin.

The Canadian Embassy here had no information on the "Crisis in Rain" film, which apparently was not produced by its national film board but by an independent film producer for the Ontario Ministry of the Environment.

The brouhaha hit the State Department at a particularly sensitive time, two days after Secretary of State George P. Shultz announced an $85 million overseas propaganda effort with the words: "Don't be nervous about democracy, about holding that torch up there."

A State Department spokesman declined to comment on any "diplomatic exchanges" over the films. Shultz, questioned at a news conference in Florida, said he didn't know enough about the situation to make a "definitive comment."

"Obviously, we must stand always for the principles of freedom of expression," he said. "But where that leads you in this particular case, I'm not ready to say."

The ACLU's New York office called the decision "blatantly unconstitutional" and said it would file suit on behalf of theater owners and distributors to prevent the government from collecting the names of organizations interested in showing the films.

But even as the ACLU prepared to fight the list, a host of leading members of Congress were vying to be at the head of it.

The Senate Environment and Public Works Committee held a screening in the Dirksen Office Building, and Sen. Edward M. Kennedy (D-Mass.) announced that he intends to show the films to all his colleagues on the Judiciary Committee. Rep. Edward J. Markey (D-Mass.) said he plans to put all three films on the closed-circuit television system that feeds into every congressional office.

"It is one thing for the right wing to say 'Let Reagan be Reagan.' But it is a very different thing for them to say 'Let Reagan be Orwell,' " said Kennedy, who showed up at the National Press Club yesterday to introduce Dr. Helen Caldicott, a prominent nuclear freeze advocate who is featured in one of the films.

That film, "If You Love This Planet," has been nominated for an Academy Award, and one of the acid rain films, "Acid Rain: Requiem or Recovery," won top honors last year in competition sponsored by the American Society of Foresters.

Kennedy also said that he wanted Attorney General William French Smith to appear before his committee "to explain this inexcusable action by the department he manages."

The administration has opposed an arms freeze, as well as stringent air pollution controls to curb acid rain. Environmentalists and nuclear freeze advocates have accused the administration of attempting to prevent the flow of information on the subjects.

But a statement released yesterday by Justice spokesman Thomas P. DeCair defended the action as a "routine" decision "made solely by career attorneys" who enforce the Foreign Agents Registration Act. The Canadian film board, a cultural agency supported by its government, is registered under the act.

The Justice statement said that about 50 percent of the 25 or more films it reviews each year "are found to be within the statutory disclosure requirement." Film distributors and ACLU attorneys, however, said they were aware of only one similar case, an unsuccessful attempt in the mid-1970s to impose some restrictions on a showing of Cuban films.

The foreign agents law defines "political propaganda" in part as any communication intended to "prevail upon, indoctrinate, convert, induce or in any other way influence . . . any section of the public within the United States with reference to the political or public interests, policies or relations of a government of a foreign country."

Justice spokesman John Russell said Thursday that the definition was broad enough to include "a film about a country that boasts good seaports and low taxes."

DeCair's statement said that department attorneys make their decisions "based primarily on common sense."

To which the ACLU responded: "The last one to use common sense effectively was Thomas Paine." Paine, a Revolutionary War pamphleteer, wrote "Common Sense" in 1776, calling for the independence of the colonies from Great Britain. The pamphlet, which had a profound effect on public opinion and the Continental Congress, sold 100,000 copies in three months.