The Justice Department yesterday defended its decision to label as "political propaganda" three Canadian films about acid rain and nuclear war, saying politics played no role in the decision.

D. Lowell Jensen, assistant attorney general in charge of the Criminal Division, told the House civil and constitutional rights subcommittee that the action was necessary under a 40-year-old law that requires any film sent to this country by a registered foreign agent--such as the National Film Board of Canada--to be labeled if it engages in political advocacy.

"It is of no concern whether the advocacy is from friend or foe, or whether it promotes or attacks U.S. policy," he said.

The Justice Department decision last month triggered a public outcry and charges of political censorship. The American Civil Liberties Union has filed a lawsuit to block the action, saying it violates constitutional free speech guarantees and stigmatizes the films.

The decision on the films was made by Joseph Clarkson, a career government employe who has spent 10 years in the foreign agent registration unit of the Criminal Division.

Asked why he chose those films and none of the 59 others on the semi-annual list sent by the Canadians, Clarkson said, "It was picked because we keep an eye on what issues are important as far as Congress is concerned. We know nuclear disarmament is an issue. We know acid rain is an issue." Clarkson denied that there was any pressure from the administration, which is especially sensitive about those two issues. "Until the day the stories started hitting the papers, I doubt there was anyone else excluding myself and two others in his division who knew anything about the films," he said.

By law, a film judged to be political propaganda must carry a disclaimer saying it was produced by a party registered as a foreign agent and that "registration does not indicate approval of the contents of this material by the U.S. government."

There is no requirement that films carry a label that the Justice Department considers them "political propaganda." The Justice Department requires the "foreign agent" distributing the film to provide the names of any group or theater that shows the film, the dates it is shown and the number of people in the audience.

The names of those groups or theaters are then put into the files of the Justice Department's Criminal Division as receivers of foreign "political propaganda."

Rep. Don Edwards (D-Calif.), subcommittee chairman, questioned the need for the labeling procedure, calling it "a little paternalistic."

The subcommittee is expected to consider legislation introduced by Rep. Robert W. Kastenmeier (D-Wis.) to remove the requirement.

Clarkson testified that he doesn't know how many films come into his office for review each year, but congressional aides place the figure as high as a thousand or more. He said that the initial review is done on the basis of titles alone.

The three films were "If You Love This Planet," on the medical consequences of nuclear war, and "Acid from Heaven" and "Acid Rain: Requiem or Recovery," on the damage caused when sulfur dioxide pollution mixes with rain to form a weak solution of sulfuric acid.

The law originally was passed to deal with the problem of German agents engaged in propaganda efforts in the United States before World War II.

Justice Department files released yesterday by Jensen indicate that in recent years six to 10 films annually have fallen into that classification, many of them appearing to deal with foreign trade.

These include "Made in Hong Kong," produced by the government of Hong Kong, and "Berlin Means Business and More," by the Berlin Economic Development Corp.