Prime Minister Pierre Trudeau, seeking to head off a crisis in Canada's troubled federal-provincial relations, has acceded to demands from the provincial governors that he not proceed immediately with plans to write a new Canadian constitution.

In an important concession to the fractious provincial leaders, Trudeau said yesterday that he is willing to delay his timetable for constitutional reform until late October to give the provinces time to prepare for a final negotiating session with him. With the delay comes the possibility that Trudeau and the eight dissenting provincial leaders might strike a compromise on the elements of a new constitution, thus averting a showdown that many Canadians fear could cause deep and lasting damage to Canada's federation.

Of the 10 provincial governments, only two -- Ontario and New Brunswick -- support the Liberal Party government's year-old drive to install a new constitution without the approval of the provinces. Among the provincial leaders ranged against Trudeau, opposition is deep-seated and bitter, a situation that gives rise to only slim hopes that the two sides will be able to reach a compromise.

Last month, the Supreme Court declared that Trudeau's constitutional plan was legal in a narrow sense. But, because of the lack of provincial consent, the plan was also inimical to Canada's federal traditions, the court said.

Heartened by this ruling, the provinces have rallied together for one last effort to alter Trudeau's proposals. Their weapon, apparently partly successful, was to force delays in Trudeau's planning, which called for the constitutional resolution to be presented to Parliament soon. The current session opened Wednesday.

Announcing his agreement to wait for another meeting with the provincial premiers before acting on the constitution, Trudeau said, "I regret that for the third time" the provinces "have found it necessary to delay our proposed first ministers' meeting." But Trudeau said he was pleased that such a meeting now appears likely, and named Oct. 26, 27, and 28 as possible dates.

A final date cannot be set until after the premiers meet among themselves early next week.

Trudeau's willingness to wait out the premiers represents a striking shift from his government's position after the Supreme Court decision was revealed Sept. 28. Then, the Liberal government vowed to proceed quickly with its plan for constitutional change on the ground that it had been given the legal go-ahead by the high court.

Canada's current governing charter, dating from colonial days, is an act of the British Parliament. Trudeau wants Britain to transfer the constitution to Canada, complete with a new Bill of Rights and a formula for making future amendments. The provinces oppose the latter two items as infringements on their powers.