THE PROVINCE of Quebec is now going to attempt to enforce the use of the French language increases the unfortunate possibility that Canada might actually break apart. Prime Minister Pierre Trudeau has been trying to hold the country together with the principle of bilingualism, allowing Canadians to use whichever language they choose. But the separatist government of Quebec derides the choice as an empty one, as long as careers at the top in Montreal's business and professional world require English. The soulution, the separatists say, is to make big business speak French when it comes into the province. "There will no longer by any question of a bilingual Quebec," the provincial government stated last month in its White Paper.

Companies with more than 50 employees will be given six years, according to the White Paper, to get their certificates of francization. The objective here, it explains, is to assure that the executives of companies in Quebec acquire "satisfactory" French - and use it on the job. Failure to get certification would mean fines and loss of licenses. Doctors, lawyers, and engineers will also have to pass French tests to get their professional licencses. Last week the provincial government began pushing the implementing laws through its legislature.

Five-sixths of the province's people speak French as their English-speaking middle class, and the city is the headquarters of a long list of national and international corporations and banks. Since three-fourths of Canada as a whole speaks English, the language inside these national organizations is English, and a young Quebecois won't get far in them without it. "In business," as the White Paper accurately states, "French to a very great extent is the language of inferior jobs and low incomes." The solution? Make business speak French all the way to the top. The obvious price would be an exodus of companies to Toronto. The national government says it's already begun.

The separatist movement in Quebec is being driven, you might say, by the heat of a genuine social revolution among French Canadians. Until very recently, around 1960, most of French Canada lived a life that turned intensely inward. On April 17, incidentally, this newspaper's Outlook section published a description of that life by the Quebecois writer and critic Robert Scully; it promptly brought a torrent of denuciation down on Mr. Scully in Montreal. But for American readers the essay offers an invaluable - and moving - piece of the explanation of what's happening there today.

In 1960, the typical French-speaking Canadian had left school much earlier than his English-speaking counterParts: he was more likely to live in the country, work with his hands, go to church regularly, and rear a large family. But that's all changing with tremendous speed. One striking index of the swing in mores is the drop in the French Canadian birth rate, which used to be one of the highest in North America and is now one of the lowest. French Canada used to trust its birth rate to guarantee its survival. Now French tradition feels sharply threatened by small families and a tide of immigrants who want their children to learn English in order to rise in the world.

Quebec's language legislation is, in effect, a declaration of cultural independence. It is a rejection of the hope that people using different languages can live together in equality and concord. It is an explicit challenge, a little earlier than expected, to Mr. Trudeau and the federal government of Canada.