A prominent Canadian wildlife writer was refused entry to the United States this week under a U.S. immigration law barring communists and anarchists, while a Nicaraguan cabinet minister was forced to cancel the start of a 10-day speaking tour because of delays caused by the same provisions.

Canadian author Farley Mowat, who wrote the best-selling "Never Cry Wolf," said he was stopped from boarding a flight to Los Angeles Tuesday at Toronto International Airport.

Nicaragua's minister of culture, poet-priest Ernesto Cardenal, meanwhile, was prevented from delivering a speech at a University of Kentucky modern language convention last night while U.S. officials considered his week-old request for a visa.

The actions focused fresh attention on the 1952 McCarran Act, which critics contend has been used by the Reagan administration to "shape and limit political debate within the United States." The act bars entry of communists, anarchists and like-minded advocates.

According to Mowat's U.S. publisher, Harry Evans of Atlantic Monthly Press, the Canadian was headed for a series of West Coast stops to promote his newest book, "Sea of Slaughter," which depicts the destruction of seacoast wildlife in Canada and the United States.

"They [U.S. officials] suggested I meet with them in the middle of the Peace Bridge over the Niagara River, on neutral ground, and then they would review my dossier with me, but with no guarantee," Mowat said from Toronto yesterday in a telephone interview.

"I told them, as any red-blooded Canadian would, to stuff it."

U.S. Immigration Service spokesman Duke Austin said Mowat had been listed for years on the agency's "Lookout Book," a compilation of tens of thousands of names of people deemed inadmissible, from criminals to communists.

Austin said that the grounds and date for Mowat's listing are "confidential," but that they related to at least one of three sections of the McCarran Act.

One, Section 27, deals with individuals suspected of planning to do something "prejudicial to the public interest" or dangerous to "the welfare, safety or security of the United States."

The second, Section 28, is the "anarchist-communist umbrella."

The third, Section 29, involves espionage and sabotage and, specialists say, generally is reserved for actual spies.

"We're not going to divulge which ones" might apply to Mowat, Austin said.

But he said the author would be told if he wanted to meet with officials on the Peace Bridge and have a chance to rebut the allegations.

"No bloody way," Mowat said. "It's not up to me to prove my innocence. If they want to come to me and make explanations, I will permit them to come to my house, but that's as far as it goes . . . . I may have met lots of anarchists and I have certainly met lots of communists, but I am not a member of any subversive organization and never have been."

Mowat said he had entertained Soviet writers in his home, visited the Soviet Union in 1967 and 1969 for research on a book about Siberia and was once a member of the Fair Play for Cuba Committee.

A Justice Department source yesterday said one reason for denying Mowat entry was a March 22, 1968, Ottawa Citizen news article in which Mowat was quoted as saying he had fired at U.S. planes with a .22-cal. rifle because he didn't want them flying over Canada with hydrogen bombs.

Mowat, who spoke to The Washington Post before the statement from the Justice Department source, could not be reached again last night for comment.

Cardenal, according to a Nicaraguan Embassy spokesman here, last visited the United States in late November for a speaking tour that lasted about two weeks.

He had planned to give a series of poetry readings and talks beginning last night in Kentucky and continuing in Colorado, New York and Massachusetts.

He applied for a visa April 17 but was told several times that it was not yet "authorized."

"One thing they said was that he was a member of the World Peace Council and they had a 14-day waiting requirement," said Nicaraguan Embassy counselor Roberto Vargas.

State Department spokesman James P. Callaghan said Cardenal's visa request was "still under review" under Section 27.

Such applications are reviewed each time to see if there are "changed circumstances," Callaghan said.