TORONTO, JUNE 9 (SATURDAY) -- Canada's 10 provincial premiers and Prime Minister Brian Mulroney reached an agreement in principle early today on a fragile compromise package of constitutional changes designed to stem a growing separatist movement in the predominantly French-speaking province of Quebec.

Following six days of marathon negotiations in Ottawa, Mulroney and the provincial leaders said they will meet again later today with lawyers to put the finishing touches on the accord. One premier, Clyde Wells of Newfoundland, said he would press for restoration of some language that had been agreed to in a previous text.

Mulroney had earlier described the draft accord as a "fish-or-cut-bait" set of proposals. He said if they were rejected, the unity of the 123-year-old Canadian confederation would be seriously threatened.

Mulroney and the provincial premiers emerged from a 13-hour, closed-door meeting early this morning to announce the accord. Mulroney said it "appears to be a very, very good development for Canada, for all Canadians, and completes a very important constitutional process in making this country whole again."

"The mission is accomplished," Quebec Premier Robert Bourassa said. "It is a very great day for Canada."

The package preserves an earlier set of constitutional amendments initialed by federal and provincial leaders in April 1987 at Meech Lake, Quebec, but later rejected by three provinces. Unless approved by all the provinces before June 23, the amendments will expire.

The key provision of the 1987 accord was constitutional recognition of Quebec as a "distinct society" -- a clause that the province said was necessary for it to sign Canada's 1982 constitution.

The compromise provides that constitutional experts will draft an explanatory statement to the effect that the distinct-society clause does not undermine Canada's bill of rights, which had been a principal objection of the holdout provinces of Manitoba and Newfoundland.

Under their provincial laws, both Manitoba and Newfoundland will have to ratify tonight's agreement and the original Meech Lake accord in their legislatures. In Manitoba, where Premier Gary Filmon heads a minority government, the legislative debate could be contentious, political analysts said.

The clarifying statement appeared to have little legal weight and will not even be signed by the premiers, but apparently was designed to allow Quebec Premier Bourassa to reassure his constituency that the Meech Lake accord was not changed, while at the same time allowing the holdout premiers to go home saying it was.

Thursday night, Bourassa, who has been under intense pressure by militant separatists in Quebec, said he would no longer participate in any discussions that touched directly or indirectly on the distinct-society clause.

The compromise also contains a commitment by the premiers to hold public hearings on the definition of Canadian identity and hammer out a clause to broaden that definition and explicitly recognize the multicultural character of the country and the equality of its provinces.

The effect of the clause is to recognize that a number of distinct societies besides that of the French Canadians exist, including those of aboriginal Indians and Eskimos, and that no ethnic or cultural group is excluded from the constitution.

The premiers also committed themselves to reform the appointed Senate chamber of Parliament by making it an elected and more effective body with greater equality of representation by the provinces. The premiers reported that, under the agreement, Nova Scotia, New Brunswick and the populous province of Ontario will give up seats in the 104-member Senate. The other provinces, except Quebec, will get more seats. Currently, Ontario and Quebec each hold 24 seats in the Senate.

The breakthrough came after the meeting was on the verge of breaking up in disarray over Mulroney's final compromise package, but Ontario Premier David Peterson offered to win Newfoundland Premier Clyde Wells' approval by giving up six of his province's 24 seats in the Senate.