An historic attempt to mold a new Canadian constitution ended in failure here today, as talks between Prime Minister Pierre Trudeau and the country's assertive provincial leaders broke off without agreement.

Rather than relieving Canada's growing internal tensions, as had been hoped, the talks seemed only to further the regional and cultural differences that have blocked attempts for 50 years to produce a new Canadian governing charter.

Trudeau, whose administration is deeply embroiled in political struggles with the French-speaking province of Quebec and the resource-rich provinces of the vast Canadian west, voiced concern in today's closing session about the future viability of the Canadian federation.

Calling the negotiations a "failure," Trudeau wondered aloud if Canadians had just seen "the beginning of the end of a Canada torn between two different concepts" of government.

He was referring to the main stumbling block in the talks -- the clash between his government's vision of Canada as a federation with a strong central government and the provinces' conception of the country as a loose association of strongly autonomous provincial governments.

Appearing bitter and combative, Trudeau reiterated his contention, made repeatedly during the week, that Canada is already the world's most decentralized federation. He characterized the stance of the provinces as "an ultimatum for more provincial power" to which he could not accede.

Canada's current constitution is an act of the British Parliment adopted in 1867. Since ceasing to be British colony in 1931, Canada has had the right to "bring home" this document, but it has not done so because of an inability to read agreement between Ottawa and the provinces on amending a new Canadian charter.

Trudeau refused to say after the conference if his government would follow through on its earlier threats to devise a new Canadaian constituttion on its own by the end of this year if there were no agreement in these negotiations.

This threat has drawn sharp criticism from the provinces, and today some provincial premiers warned Trudeau against such action. Premier Rene Levesque of Quebec said he would find such action by the fedeal government "totally acceptable" and would oppose it vigorously.

How much of a furor would ensue if Trudeau carried out his threat would depend in part on how he approaches the British government. If he simply asked that Canada's constitution be returned -- a move that had been widely supported by Canadians for years -- then provincial reaction might be moderate, observers believe.

If Trudeau attempted to insert into the new constitution an amending formula and a bill of rights, however, the provinces probably would set off a major political row. That would likely include a challenge in the Canadian courts and intensive lobbying of the British government.

A confrontation with the provinces over the constitution might further destabilize Canada, which has already skirted to major crises recently. Earlier this summer the government of Alberta challenged Ottawa's right to set the price of domestic oil, setting the stage for a conflict that could further strain Canada's government system this fall. In the spring Canada turned back a drive for independence in the French-speaking province of Quebec that threatened to break up the country.

During the week, trudeau and his provincial counterparts failed to reach significant compromises on most of the 12 constitutional topics under discussion. On the issue most important to Trudeau -- a new bill of rights that would protect democratic, language and other freedoms -- the provincial governments mounted a solid wall of opposition, with seven out of 10 provinces objecting strongly to the proposal.

The governments came close to agreement on a handful of topics, and some provincial premiers said further discussions should be considered at an early date.