FOR many Canadians, the idea that their country risks violence or even civil war if Quebec parts company with Canada is anathema - simply not worth discussing.Yet some have begun to think aloud about the unthinkable: the seemingly remote possibility that Canadians could find themselves fighting former Canadians. Several scenarios lurk behind the polite, albeit intense national debate over how to resolve the constitutional crisis and entice independence-minded Quebec to stay. If Quebec leaves, security analysts say, it will almost certainly form a military force to protect its sovereignty. "People haven't really come to grips with the impact of an independent Quebec," says Desmond Morton, professor of military history at the University of Toronto. "English Canadians think it's alarmist to talk about it, and Quebeckers say [separation] would work out nicely because Canadians are such reasonable people. But what is happening in Croatia is not absolutely unthinkable here." Perhaps not, but it has been virtually unmentionable. Despite their gravity, security issues and potential areas for armed conflict have remained largely unmentioned in public forums until broached here Nov. 6 and 7. A conference of 200 military and national security experts from across Canada garnered headlines like the one in last Monday's Toronto Star: "Can We Really Rule Out Civil War?" Especially among politicians trying to forge a new constitution, there seems little appetite for publicly discussing how separation would affect Canada's international security arrangements in groups like NATO and NORAD. There is even less relish for analyzing areas of potential conflict with a sovereign Quebec: territorial and border disputes, calls from native or English-speaking Quebeckers for Canada to rescue or defend them, even airspace and fishing rights off Quebec's coastline. Assembly of First Nations Chief Ovid Mercredi, who represents about 500,000 of Canada's Indians, has warned that natives who inhabit large areas of Quebec may not go along with separation. "This is the first public discussion. No one has ever talked about national security [following separation] in part because Canadians don't want to think about the country breaking up," says Alex Morrison, executive director of the Canadian Institute of Strategic Studies, which hosted the conference. Reflecting the political delicacy of the current attempt by the federal government to sell English-speaking Canada, Quebec, and natives on a single constitutional plan, government officials declined even to indicate whether the government has ever discussed the ramifications of separation. A spokesman for Canada's Department of External Affairs, the equivalent of the United States State Department, said: "We're not commenting publicly on the constitutional evolution of Canada." Canadian officials are similarly cautious on the question of whether Canada's soldiers might be affected by conflicting loyalties in the event of a split. "I think the fact that the armed forces of Canada is the best example of unity in action speaks well for the way we have assimilated English and French into an organization that works extremely well," Robert George, deputy chief of the Defense Staff, told the Monitor. None appeared more taken aback by press reports of the conference than Francine Lalonde, third in command of the Parti Qucois (PQ), the pro-sovereignty party that has gained a wide following in Quebec. She echoes party leader Jacques Parizeau's vision of a peaceful transition to nationhood. The conference "was quite frightening for us," says Ms. Lalonde in a phone interview. "It is a strange feeling we get here. I think I can say with some strength that the PQ and the sovereignists want a peaceful, democratic way of getting our own way." Still, Lalonde reiterates that a peaceful, sovereign Quebec "does not mean lack of defense." Quebec will possess conventional, but not nuclear, military forces, she says. The PQ may gain by speaking softly on security issues at this point, some analysts say, to avoid frightening those who might favor Quebec sovereignty in a referendum slated for fall 1992. Mr. Morrison says he is "fairly confident" the PQ has been "looking for some time" at the structure and cost of a Quebec military, and may even have drawn up a list of names of those who would command such a force. But it is possible the PQ is even farther along in its planning. A source with links to the PQ told the Monitor that since January the PQ has actively engaged in developing a blueprint for a national military. The source says the party has considered a force of 30,000 to 50,000 men, with as many as 50 multiple-use fighter aircraft, icebreakers, patrol boats, and other ships, and a cost estimated at $5 billion to start. When asked if it was true the PQ had reached a level of specificity that included the cost, size, type of weaponry, and names of officers to command the force, Lalonde volunteers: "What I've heard is only conferences by specialists on that subject. By no means have I heard of meetings coming to a decison.... We know we have to listen to people like that, so it was one meeting and not more than that." For some Canadians, however, the issue of military action seemed blown out of proportion at the conference and diverted attention from other little-discussed issues - like Canada's loss of clout on international security issues if separation occurs. "The probability of a resort to force instead of negotiation to settle this problem is not high on my scale of probabilities," says John Halstead, Canada's ambassador to NATO from 1980 to 1982 and ambassador to West Germany from 1975 to 1980. "It would be realistic to face up to the dangers inherent in the situation. But to construct scenarios which envisage violent acts and the deliberate use of force is not helpful."