When Quebec's premier faces the National Press Club here next Thursday, he most certainly will be questioned about his proposed referendum on semi-independence for the province, his political relations with Canadian Prime Minister Pierre Trudeau and the French Language Law that has prompted some English-speaking companies to leave Montreal. Rene Levesque, 56, a former television moderator who is regarded by supporters and foes alike as a master media performer, can be expected to have reassuring words for Americans on these troublesome topics.

Since his election in 1976 on a pledge to gain th French-speaking province's independence from the rest of Canada, Levesque has moderated his stance. The referendum is expected to ask Quebec voters simply for authorization to negotiate for sovereignty-association. This would give Quebec residents the power to make all their own laws and pay only the taxes they levy. Yet there will be a common currency, joint central bank and no customs or passports required for the other provinces.

The exodus from Montreal of the head offices of companies for which English is the primary working language is said to have abated after the feared independence and language issues were defused. In December, it was announced that head offices of firms drawing more than 50 percent of their gross revenue from outside Quebec can negotiate special agreements to continue doing business in English. Moreover, children of employes transferring to Quebec will be granted a six-year exemption from attending French-language schools.

Another sensitive issue likely to come up in the press conference is Levesque's proposed expropriation of Asbestos Corp., a Canadian mining company that is 54.6 percent owned by General Dynamics, the St. Louis aerospace firm. The threat has the business community in both countries worried about other possible takeovers despite Levesque's assurance two years ago in a speech to the Economic Club of New York that his government was not planning a "policy of nationaliztion."

American businesses control about 70 percent of Canada's foreign investments and are particularly strong in natural resources. Quebec is a major borrower in U.S. financial markets, and there is also substantial American direct investment in the province. Since his election, Levesque has stumped this country seeking U.S.-Quebec cooperative ventures ranging from aid to French speakers in Louisiana to selling electric power cheaply to New England states in exchange for purchases of oil from Quebec and Maritime Provinces refineries.

How will the expropriation threat affect potential and existing investors? Guy W. Fiske, the chairman of the board of Asbestos Corp. and executive vice president of General Dynamics, said in an interview last week, "It would not be our recommendation to anyone to invest in Quebec."

However, some observers see signs that Levesque also is moderating his stand on this issue. MacLean's magazine commented last month: "Where no more than a year ago Premier Rene Levesque stood on a makeshift stage in the grimy town of Thetford Mines striking deep, cancerous chords of miner response with promises to rout the English-dominated industry, the government now seems ready to compromise with the asbestos villains."

Asbestos is a $400-million-a-year industry in Quebec, employing 6,500 workers. It accounts for 6.5 percent of the province's exports. Yet only 3 percent of the asbestos mined in Quebec is processed there, partly because the finished products are too expensive to ship. Levesque's Parti Quebecois has a goal of 3,000 new asbestos-processing jobs by 1985.

The Asbestos Corp., second only to Johns-Manville in production volume, employs 2,600 workers and produced 23 percent of Quebec's asbestos in 1977. It was selected for nationalization because it is the only company engaged solely in mining and the only one that is not an integral part of a manufacturing operation elsewhere. Asbestos Corp. has a manufacturing plant in West Germany.

General Dynamics has insisted it does not want to sell the company because Fiske claims a sale would not create any jobs and therefore would not be in the interest of the province. He now concedes selling at a fair price would be preferable to being expropriated. For the past year, Fiske and Quebec's finance minister, Jacques Parizeau, have conducting informal discussions but no negotiations have taken place or are scheduled.

The barrier is money. General Dynamics hired Lazard Freres & Co. to determine the fair market value of Asbestos Corp.It came up with a price of $99.75 (Canadian) per share, or a total value close to $300 million. Kidder Peabody & Co., hired by the province, came up with a value of $42. Fiske claims that Parizeau promised in the beginning to pay a premium for the shares, but neither side has yet made an offer.

In late fall, Quebec set up the Societe Nationale de l'Amiante (the National Asbestos Corp.) to take over the public corporation. On Dec. 15, a bill was introduced into Quebec's National Assembly to expropriate the company's assets. Parizeau said the action was taken "given the impossibility of discussing with the other party on a rational and concrete basis the nature of the presumably substantial gap between the prices suggested by the two studies." Fiske accused Parizeau of "putting a gun in our ribs."

An expropriation price would be fixed by an arbitration board composed of three members: one from the Societe, one from Asbestos Corp. and one from the provincial government. The price paid would be that at the time the Societe became the owner. General Dynamics think the price should be based on asbestos reserves in the ground.

No action was taken on the bill, and Fiske says he has Parizeau's word that none will be taken in the rump session in February. However, were the government to decide to put it to a vote, it would pass easily. It would have to be reintroduced in the next session beginning in March. "I don't think they want to expropriate if they can find a politically acceptable price," said Fiske, adding, "The ball is now in their court."

Fiske hinted General Dynamics still has more than one card up its sleeve. He said there is little the company could do to stop passage of legislation, but its lawyers are exploring legal action to stop actual expropriation. Although he refused to divulge strategy, he did say that because Asbestos Corp. is chartered by the federal government of Canada and because its manufacturing plant is outside the country, he feels it would be unconstitutional for the provincial government to expropriate the firm.