A U.S. Court of Appeals panel here, in a strongly worded opinion by Judge Antonin Scalia, has ruled that the federal government has the constitutional right to label as "political propaganda" three Canadian films, two dealing with acid rain and one about nuclear war.

The 26-page opinion by Scalia, whom President Reagan this week said he will nominate to the Supreme Court, noted that the panel's finding was at odds with that of a federal judge in California who ruled last year that the labeling was unconstitutional, saying that "to characterize a particular expression of political ideas as 'propaganda' is to denigrate those ideas."

The Supreme Court has agreed to hear an appeal of the California ruling in the coming term. It is not known if Scalia, should he be on the court then, would participate.

Chief Justice of the United States Warren E. Burger and Associate Justice Harry A. Blackmun have disqualified themselves from cases in which they had participated as appellate judges, court officials said, but there are cases in which appeals court judges have participated in decisions on rulings they made at the district court level.

Scalia was joined in his opinion, which was issued Wednesday, by Senior Circuit Judge J. Skelly Wright and Judge Robert H. Bork.

The case, brought by the American Civil Liberties Union and Mitchell Block, president of Direct Cinema Ltd. Inc., the films' distributor, involves a 26-minute Academy Award-winning documentary titled "If You Love This Planet," which features a lecture by antinuclear activist Dr. Helen Caldicott, and two films on the environmental hazards of acid rain, titled "Acid From Heaven" and "Acid Rain: Requiem or Recovery."

The Justice Department ordered the films labeled "political propaganda" in 1983 under the 40-year-old Foreign Agents Registration Act and required that when shown in this country they carry a disclaimer that the U.S. government does not approve of them.

Under the act, Direct Cinema also was required to report theaters or groups that showed the films and any group that purchased 100 or more copies.

The ACLU and the films' distributor contended that the labeling and reporting requirements would discourage groups from buying or showing the films.

U.S. District Court Judge Charles R. Richey dismissed the suit here, saying the parties had not shown they would be damaged by the requirements.

"In short, it seems to us that in labeling something 'propaganda' the government is not expressing its own disapproval but is merely identifying an objective category of speech of which the public generally disapproves," Scalia wrote in his opinion.

" . . . We know of no case in which the First Amendment has been held to be implicated by governmental action consisting of no more than governmental criticism of the speech's content," the opinion stated. " . . . A ruling excluding official praise or criticism of ideas would lead to the strange conclusion that it is permissible for the government to prohibit racial discrimination, but not to criticize racial bias; to criminalize polygamy, but not to praise the monogamous family; to make war on Hitler's Germany, but not to denounce Nazism."