Quebec Premier Rene Levesque, in an effort to gain American support for plans to turn his province into a sovereign nation, asserted yesterday that an independent Quebec would become a "staunch partner" in the Western alliance.

In major attempt to explain the program of his separatist Parti Quebecois, Levesque said at a National Press Club luncheon that an independent Quebec would maintain its own military forces but would assume security responsibilities in cooperation with the United States and Canada.

"I ask you to understand that Quebec is going to remain a strong, staunch partner on this continent," he said. "One thing that we would not change is the old friendship with the Americans."

In tone, if not in substance, his speech suggested a stronger commitment to common strategic interests in North America that was apparently tailored for an American audience.

Buttressing this view were Levesque's lengthy references to the "common heritage" that Americans and French-speaking Canadians share. He said the Quebecois now want to resume their natural development which was halted "200 years ago when Quebec was conquered" by the British.

He made it clear that his party's aim is political independence for Quebec. He said the relationship between Quebec and the rest of Canada would be similar to the envisioned for members of the European Economic Community -- sovereign nations sharing a common market and joint currency.

The issue of whether the Quebecois support his concept, Levesque said, will be decided "democratically" in a province-wide referendum to be held within the next 18 months.

Levesque's visit here is part of his government's full-scale compaign to persuade his constituents to endorse the concept of "sovereignty-association" for Quebec.

Since polls have indicated that a clean break from Canada would not win in the planned referendum, Levesque is planning to ask the electorate for a mandate to negotiate the two issues simultaneously-seeking sovereignty and a continued economic association with Canada. The linkage implies that the Quebecois would have nothing to loose if they back Levesque in the referendum.

The visit here coincided with the publication in Canada yesterday of a report saying that the Canadian federation is faced a breakup and proposing a major overhaul of political institutions to help weather this "crisis of existence."

The changes proposed by the Task Force on Canadian Unity include a proportional representation system for the House of Commons; increased authority for the Senate, whose members would be appointed by provinces alone; a special status for Quebec in the cultural area; granting provincial governments authority to develop and implement language and educational policies; and giving Quebec 5 of 11 seats on the Supreme Court (instead of three out of nine at present).

Asked about the report, which appeared to meet many French Canadian grievances, Levesque would say only that it was by no means certain that it would be acceptable to English speaking Canada. He added, "This is a sort of half-way house."

"We are strongly convinced that whenever you have two different national entities, the classical federal system will not work," he said.

"We are going to propose that we opt out" of Canada which "has become for us a sort of straight jacket, certainly hampering, limiting our development."

His "soverignty-association" plan, he said, would "permit us to build a new, better rapport between our two societies, even become friends which we have never been."

The National Press Club address and an appearance last night on public television's McNeil-Lehrer Report were Levesque's principal appearances during a day of meetings which included a session with Sen. Edmund Muskie (D-Maine) and students and faculty of Georgetown University.

Levesque did not meet any administration officials because that would have required the involvement of the Canadian Embassy here, which he studiously sought to avoid.

His references to Quebec's own military force seemed to add a new note to his well-publicized positions. Asked if Canadian troops would be present in an independent Quebec, Levesque quipped, "only as tourists."

"We would like to have and we intend to have our own forces," he said. But he said security arrangements in NATO would continue since "we are in a world of security arrangements."