A ''deeply troubled'' Canadian Prime Minister Pierre Trudeau has embarked on his greatest, and perhaps last, political venture. Announcing a personal peace plan that will see him visit five European heads of state in a four-day visit early next month, Trudeau said it is time in his career for ''creative radicalism in a very important area, disarmament and the pursuit of peace.
''There is a climate of acrimony that is dangerously confrontational. Their (the superpowers') relationship may have become too charged for East-West relations to be entrusted to them alone.''
His plan drew an immediate reaction. The United States Embassy in Ottawa issued a statement cautioning Trudeau against over-involvemnt in nuclear arms control talks between the superpowers. ''In dialogue with the East on arms-control matters, the chances for genuine progress in these negotiations will be strengthened if Soviet leaders come to understand that the allies are united on such common security issues as INF (intermediate-range nuclear force) negotiations,'' the statement said.
Trudeau's longstanding sincerity on the issue is roundly acknowledged. But his peace campaign has important political implications at home, where the percentage of public support for his Liberal Party has fallen to the mid-twenties, some 30 percentage points lower than the opposition Progressive Conservative Party. He has faced close questioning in Parliament on foreign policy matters from Brian Mulroney, newly elected Tory leader, whom Trudeau is portraying as a cold warrior.
Mr. Trudeau, who promised in 1980 to retire before the next election, is not expected to do so until he has reached a position of conspicuous achievement or political strength. The prime minister's reputation and experience in the international arena, given even a moderate appearence of success in the coming weeks, are seen by party insiders as a last Liberal hope.
The Canadian peace initiative, which will take Mr. Trudeau to France, The Netherlands, Belgium, Italy, and West Germany, was only partially welcomed by representatives of Canada's increasingly strident disarmament movement. Mr. Trudeau chose an international disarmament conference at the small Universirty of Guelph, Ontario, to deliver late last week the speech that contained initial details of his plan. His critique of the superpower impasse was carefully applied to both superpowers, but he was plainly critical of President Reagan: ''I am not reassured by the posture and rhetoric of an earlier wartime age. Both Washington and Moscow seem to lack a political vision of the world wherein their nations can live in peace.''
He was careful to defend his government's decision to allow the US to test air-launched cruise missiles in Canada's north this winter, a matter that has brought hundreds of thousands of Canadians onto the streets in protest. He also affirmed the commitment of NATO leaders to the ''two-track'' policy of negotiations and deployment that will most likely lead to the installation this winter of the first of 572 cruise and Pershing missiles in Europe.
Canadian officials are privately doubtful that Mr. Trudeau will be able to insert himself as a go-between at the superpower negotiations. Trudeau sees his efforts as a ''third rail for the two-track decision - the third rail which might speed the course of agreement.''
He has shown in the past that he can be consumed by single issues - North-South relations and the repatriation of Canada's constitution from the United Kingdom being prime examples - and his office says his peace effort consumes an increasing share of his attention. This devotion carries the risk of a backlash at home, where he could be seen as avoiding the domestic situation.
Trudeau's detailed strategy is being kept under wraps. He has begun ''a process of close discussion'' with President Reagan and sent messages to all NATO heads of government. He plans to raise the issue at a November meeting of the heads of Commonwealth governments in New Delhi, and may then accept an invitation to go to the Soviet Union that was made earlier this year.
But his general intentions were clearly stated in his announcement: ''What is missing are steps, a jolt of political energy, that build an authentic confidence in man's ability to survive on the planet.'' It's a jolt Trudeau hopes to provide.