Canadian Prime Minister Pierre Trudeau, in his most critical remarks to date about President Reagan, has said the U.S. leader has provided some justification for public fears that he is too "warlike" toward the Soviet Union to be trusted.

The comments, in an interview published here today, came two weeks before Trudeau is to represent Canada at the economic summit meeting of seven major western industrial nations at Williamsburg, Va.

Trudeau also expressed serious concerns about Reagan's approach to dealing with Moscow, questioned the wisdom of economic sanctions and ridiculed the notion that a nuclear war could be won by U.S. forces.

Trudeau, who has been pressured by mounting protests against the testing of American cruise missiles in Canada, said most of the demonstrators are concerned about U.S. attitudes toward nuclear weapons.

"They are demonstrating against what they see as the policy of an American president who has, rightly or wrongly, been perceived as warlike or so hostile against the Soviet Union that he can't be trusted," Trudeau said.

He added, "Unfortunately, President Reagan and some around him have given some justification for those fears."

The interview was printed in the Toronto Star, which has strongly opposed cruise missile testing in Canada. The paper displayed Trudeau's comments prominently on the front page under the headline: "Fears of Reagan Justified: PM for prime minister ."

Referring to discussions in the Reagan administration about the possibility of winning a nuclear conflict with the Soviets, Trudeau said such ideas are "pretty absurd." The point is not winning or losing but that "we want to avoid a nuclear war," he said.

Saying that Reagan, in a recent speech, had described the Soviets as "something worse than an immoral people," Trudeau said: "I disagree with so much of the approach of his administration to the Soviet Union. I think the Soviet Union is a great power, and it should be treated as a great power.

"The United States should be dialoguing with the Soviet Union and not treating them as a criminal people," Trudeau said. "They have spheres of influence and strategic points they want to defend."

Trudeau, while repeating his long-held opposition to nuclear weapons, said the U.S. cruise missile may have to be tested over Canada as part of that country's commitment to the North Atlantic Treaty Organization.

As he did last week, Trudeau accused Canadians protesting against cruise missile testing here of "hypocrisy" because, he said, they want to be protected under the U. S. nuclear umbrella without assuming responsibility for weapons development.

Trudeau also laid much of the blame for the arms race on the Soviets. Although acknowledging that he was once a "peacenik," Trudeau said he wants to dispel the notion sometimes expressed by his conservative opponents that he is not a strong defender of the United States or that he is overly sympathetic to the Soviet Union.

Trudeau also said that at Williamsburg he would seek $82 billion in fresh funds to help financially troubled Third World countries. He said most of the money would have to come from the International Monetary Fund but that $20 billion would have to be provided by private bank loans.