Premier Rene Levesque of Quebec, the champion of French Canadian independence, swept back into office today with an overwhelming victory in elections for the provincial legislature.

The unexpectedly strong win was a resounding vote of confidence in Levesque, whose goal of creating a sovereign Quebec had suffered a major setback in a referendum less than a year ago.

His comeback was based largely on a pledge to set aside the independence drive in the new four-year term of office. But by giving Levesque's nationalistic movement renewed momentum, the election result nevertheless promised continued tension between the French-speaking province and Canada's English-speaking majority.

Unofficial returns broadcast by CTV television gave Levesque's Parti Quebecois 80 seats in the 122-member Quebec legislature. The Quebec Liberal Party, led by Claude Ryan, earned 42 seats. The once-powerful Union Nationale, which held five seats, was shut out.

A high turnout of voters, estimated at more than 80 percent of the province's 4.4 million eligible voters, was recorded.

"We are no longer an accident of history," said Levesque tonight, suggesting his reelection gave legitimacy to a party whose rise to power in 1976 troubled many Canadians fearful it could bring on a battle over the Canadian constitutional system.

Ryan, in conceding defeat, said that despite Levesque's promise not to hold another sovereignty refendum, the threat of the Pari Quebecois' independence goal remains.

"We will keep walking a tightrope of uncertainty," he said.

Since he took office in 1976, Levesque's nationalist policies have driven some large corporations out of the province, kept Canadians worried about the unity of their federation and complicated the effort by Prime Minister Pierre Trudeau to win provincial acceptance of his plans for a new constitution.

Levesque, 58, has been one of the most ardent advocates of the notion that Canada's provinces must have more powers if the nation's federal system is to accommodate the country's many diverse regions with their special interests.

This stand has put Levesque in constant conflict with Trudeau who argues that further devolution of authority to Canada's already powerful provincial capitals will hasten what he sees as a process of Balkanization.

In the past year, the focus of this debate has been Trudeau's attempt to establish a new Canadian constitution with which the prime minister hopes to unify the nation. Levesque has joined seven other provincial leaders in opposing Trudeau's constitutional proposals in the courts.

The Parti Quebecois' ascendancy was the culmination of decades of resentment among Canada's French-speaking minority, concentrated in Quebec, against the nation's English-speaking majority. But when Levesque's proindependence policy was tested in a historic province-wide referendum last May 20, voters soundly rejected a plan for a sovereign Quebec linked to Canada's other nine provinces only through economic union.

In disarray after that defeat, the Parti Quebecois was given little chance of winning a provincial election that by law had to be called some time during the following year.

Until recently, the Liberals had seemed destined to form the next goverment in Quebec City ever since Ryan took over the provincial wing of the party in 1978. The 56-year-old former publisher of the scholarly Montreal daily Le Devoir successfully overhauled his party's image, which had suffered from corruption scandals in previous years.

He also helped the Liberals in Quebec win a string of 11 victories in provincial by-elections and spearheaded the provincial forces that, with an assist from Trudeau, won out in the vote on independence last year.

Ryan has concentrated his attacks on the "abysmal state" of the provience's economy.

But the election also was tinged with the current national controversy on how power should be divided between Ottawa and the provinces in the new constitution. Trudeau wants to bring in. On this issue, Levesque benefitted from his years of staunch opposition to Trudeau's remedies for Canada's federal-provincial troubles.

When the provincial legislature was dissolved March 12, the Parti Quebecois had 67 seats, the Liberals had 34 and minor parties had nine. Today's voting was for 122 seats, 12 more than the previous legislature because of redistricting.