Prime Minister Pierre Elliott Trudeau of Canada acknowledged today that the leaders of the West's seven top industrial nations were entering their annual summit conference more divided than ever before, but he insisted that these divisions would not prevent the success of the meeting.

In an interview on the eve of his meeting in Washington Friday with President Reagan, Trudeau said that success would come from the awareness of the seven leaders, most of them new to summitry, that they cannot make economic decisions in a vacuum for the decision of one invariably effects the economies of the other six.

Trudeau, relaxed and speaking softly, made his remarks to seven journalists, one each from the countries that will be represented at the summit conference in Ottawa July 18-21: the United States, France, Britain, West Germany, Italy, Japan and Canada. He arrived in Washington later tonight.

Trudeau appeared to accept the theory that the views of the seven nations had drifted further apart since the last summit because of the election of President Reagan and his conservative government in the United States and the election of President Francois Mitterrand and his Socialist government in France. Mitterrand had already made it clear that, unlike Reagan, he believes that unemployment is a greater evil than inflation.

"We know there are differences of philosophies," Trudeau said. "What I think we will have to accept is the fact that we do not operate in a vacuum. And if we choose to use such and such an economic policy, we must take into account the effect it will have, in our interdependent world, on our partners and on each other. And I think . . . that is as important as anything."

Many of Trudeau's comments about interdependence could have been interpreted as an implied criticism of the Reagan administration, since the economic policies of the United States, the most powerful country of the seven, probably affect the others more than the other way around. Several European countries and Canada, for example, have complained about the damage to their economies caused by high American interest rates.

But Trudeau avoided any personal criticism of Reagan and sidestepped any question that attempted to draw him into a confrontation. Even on the question of American interest rates, Trudeau said, "I certainly wouldn't think that Canada and perhaps not the others would want to blame the Americans in the sense that they are the culprits of some of our own economic failing. We are all guilty of some economic failing. . . It wouldn't be fair to say it was all the fault of the Americans."

The summit conference, which will be held both in Ottawa and the Quebec resort of Chateau Montebello, will be the seventh in a series that began in Rambouillet, France, in 1975. Trudeau was invited to the second session in Puerto Rico in 1976, and the Canadians have been represented ever since.

Trudeau, with the exception of one year in opposition, has served as prime minister of Canada since 1968 and thus has been in office longer than any other participant at the conference.

Reagan, Mitterrand, Premier Giovanni Spadolini of Italy and Prime Minister Zenko Suzuki of Japan will be participating for the first time. Of those meeting in Canada, only Trudeau, Prime Minister Margaret Thatcher of Britain and Chancellor Helmut Schmidt of West Germany took part in the 1980 summit in Venice.

While in Washington, Trudeau is to meet with another visitor, European Commission President Gaston Thorn -- another participant in the Ottawa meeting.