TORONTO, JUNE 21 -- Canadian Prime Minister Brian Mulroney warned Newfoundland's provincial legislature today that a vote to reject a package of compromise constitutional amendments in a crucial session Friday would probably lead to a separatist referendum in Quebec and the "dismemberment of Canada."

But even if the Newfoundlanders heed Mulroney's plea and vote to approve the amendments, known collectively as the Meech Lake accord, the painstakingly crafted compromise may fall victim to legislative delays in Manitoba, the only other of Canada's 10 provinces that has not ratified the accord.

For a week, the Manitoba legislature's only native Indian member, Cree tribal leader Elijah Harper, blocked debate on the accord to protest omission of constitutional guarantees on aboriginal rights. Debate there was finally begun Wednesday, but all parties involved said it will be impossible to satisfy procedural rules and approve the accord by Saturday, when it will legally expire.

In his appearance today in St. John's, Newfoundland's capital, Mulroney pleaded with the 52 legislators to save the accord, which is designed to keep predominantly French-speaking Quebec in the Canadian confederation by giving it special status in the constitution as a "distinct society." Failure to do so, Mulroney said, could advance the cause of the separatist Parti Quebecois and its leader, Jacques Parizeau, who seek to hold a referendum in which Quebecers would be asked: "Do you want to separate, yea or nay?"

But many political leaders in Newfoundland, Manitoba and elsewhere in English-speaking Canada have expressed strong objections to the "distinct society" designation, arguing that it would grant Quebec special rights, privileges and powers not accorded Canada's other provinces.

Mulroney warned today that polls show nearly 60 percent of Quebecers would vote for political sovereignty for the province, and charged that Parizeau would lead the campaign for a referendum "because he's committed to the destruction of our country."

Mulroney declared further that, at a minimum, collapse of the Meech Lake agreement would result in "constitutional paralysis" and "negative signals" to international money markets and bankers because, he said, "money moves to political stability."

While there is no certainty that Quebec -- Canada's second most populous and productive province after Ontario -- would move swiftly to seek independence from the rest of Canada if the accord expires, even the most moderate provincial leaders have made it clear they will begin looking at other options for what they term "a new arrangement" for Quebec outside the existing 123-year-old confederation.

Most political analysts in Quebec -- and, significantly, many normally cautious French-speaking business leaders -- also have said that collapse of the accord would lead inevitably to a referendum along the lines of a 1980 vote on provincial sovereignty. The 1980 proposal was defeated by a margin of 60-40.

Quebec Premier Robert Bourassa said this week that his government would boycott all future constitutional negotiations and start looking at "other propositions" if the accord fails. He did not specify what options he had in mind, but said that a committee in his ruling Liberal Party already has been formed to begin studying "alternate scenarios" for Quebec.

While the militantly separatist Parti Quebecois, which held power in Quebec for nine years until 1985, has advocated a nearly total break with Canada through a unilateral declaration of independence, most Liberal Party Quebecers say they envision lengthy negotiations with Ottawa, eventually leading to vastly expanded autonomy for Quebec in some sort of loose economic confederation.

In either case, economists have warned that political instability following a collapse of the accord could trigger a free fall of the Canadian dollar, a rise in interest rates and growing nervousness in international money markets, all of which could propel the country into recession.

If Saturday's deadline passes without approval of the accord by Newfoundland and Manitoba, Mulroney would be left with several options for trying to resuscitate it, each of which presents serious legal or political obstacles. He could ask the 10 provinces to approve an extension of the deadline, but that maneuver would almost certainly be vetoed by Quebec and could face a court challenge on the grounds that it is unconstitutional.

He also could simply resubmit the amendments for approval by Parliament and the 10 provincial legislatures, which would start the clock on another three-year deadline for approval, since Parliament and the nine remaining provinces would legally have that long to ratify the amendments as soon as one province approves them. But Bourassa has ruled out restarting the amending process, telling reporters that such a maneuver would be an affront to Quebecers.

Mulroney could also ask Canada's governor-general to proclaim those parts of the Meech Lake accord that require the approval of only seven provinces -- most notably the controversial "distinct society" clause -- as part of the constitution, and then seek to reopen debate on the remaining provisions that require unanimous consent by the provinces. Such a maneuver also would bring certain challenge in the Supreme Court, but it could buy enough time for Manitoba to complete its debate on the full accord.

Mulroney, whose public approval rating in national polls already had plummeted to an unprecedented low of 16 percent before the constitutional crisis, has come under severe criticism across the country for his handling of the amendments. The prime minister, in what his critics interpreted as a boastful tone, suggested in a recent newspaper interview that he had deliberately delayed summoning the provincial premiers to Ottawa for talks on the impasse until last week in order to create a "roll-of-the-dice" crisis atmosphere to force the last two holdouts, premiers Gary Filmon of Manitoba and Clyde Wells of Newfoundland to sign the accord and put it before their legislatures.