The Justice Department has decided that three Canadian films, including a documentary on nuclear war that has been nominated for an Academy Award, are "political propaganda" and may not be shown in the United States without a disclaimer stating that the U.S. government does not approve of them.

The department also wants a list of organizations that have asked to see "If You Love This Planet," a 26-minute documentary featuring a lecture by anti-nuclear activist Dr. Helen Caldicott, as well as two films on the environmental hazards of acid rain entitled "Acid From Heaven" and "Acid Rain: Requiem or Recovery."

Department spokesman John Russell said that Justice had demanded the disclaimer and the dissemination list under the Foreign Agents Registration Act. Russell said he was told that the action was "not unique," but he said he'd never heard of its being done before.

The decision has created a furor in Canada, where officials called it a throwback to the McCarthy era and an "extraordinary interference with freedom of speech."

Environmentalists in this country accused the government of attempting to suppress information on the politically sensitive subject of acid rain, and the West Coast distributor of the nuclear war film called it a "chilling" and "scary" decision that will require him to turn over the names and addresses of every librarian, teacher or civic club officer who rents the film.

"I wish they had just called it pornography," said Mitch Block, president of Direct Cinema in Los Angeles. "Then we could distribute it in plain brown wrappers."

"If You Love This Planet" was nominated for an Oscar in the short-documentary category this month, the second year in a row that a film featuring the work of Caldicott has been put up for the prestigious award. The film is scheduled to be shown to the general membership of the Academy of Motion Picture Arts and Sciences next month.

The brief film intersperses scenes from a Caldicott lecture with footage of the Japanese cities of Hiroshima and Nagasaki after atomic bombs were dropped there in August, 1945. The film also includes footage from a World War II-era Defense Department movie starring Ronald Reagan.

In a telephone interview from her Boston office, Caldicott said she was "surprised" by the Justice Department's decision. "It was a routine speech I gave two years ago in New York," she said. "Perhaps it's the first time they've seen me give a speech."

One of the acid rain films has been in circulation in the United States for more than nine months, according to the National Clean Air Coalition, a Washington-based environmental group.

"We've been showing it a long time, carting it around to schools," said a coalition spokesman. "We've showed it on Capitol Hill two or three times; it's been at League of Women Voters meetings."

All three films were produced by the National Film Board of Canada, which is registered under the foreign agents law and routinely sends Justice a list of films currently being circulated in the United States.

According to a spokesman for the film board in Montreal, Justice officials asked to see five of the listed films last September. In January, the department cleared two of them--"War Story," a drama based on the diary of a World War II physician, and "Offshore Oil," which explores the impact of oil development on coastal towns in Norway and Scotland.

But Joseph Clarkson, who heads the foreign registration unit at Justice, decided that the two acid rain films and the nuclear war documentary fell under the "broad term of political propaganda," according to Russell. The definition used by the Justice Department, he said, "could even include a film about a country that boasts good seaports and low taxes."

But Russell said the decision was "not a move to edit or stifle" the Canadian agency. "We're certainly not trying to make it hard on the Canadian film board," he said.

He also said that Justice is interested only in general categories of who sees the film, not specific names. But Block, who has turned the matter over to his attorney, says the law requires names and addresses of viewers if a fee is charged to see the films.

The Canadian government generally distributes its acid rain films free of charge, but Block's firm charges a rental fee.

Special correspondent Les Whittington reported yesterday from Toronto that the decision had angered Canadian officials, who have been pressing the Reagan administration to adopt more stringent air pollution standards to curb acid rain damage in both countries.

Environment Minister John Roberts, whose department commissioned the acid rain films, said: "It sounds like something you would expect from the Soviet Union, not the United States." Adding to the furor in Canada is a recently signed U.S.-Canada agreement that may lead to the testing of unarmed cruise missiles over western Canada. The agreement has sparked protests from Canada's growing anti-nuclear arms movement.