In measured tones that boomed out across this snowbound land the other night, Vice President Mondale was lavishing praise on a Canadian frequently slighted by previous administrations.

Pierre Trudeau, Mondale said, is "a priceless asset to the industrialized world," a "remarkable prime minister" who as the longest-serving leader in the NATO alliance could impart "wisdom and understanding" in world affairs on the visiting U.S. dignitaries, among them three senators.

Even though some Canadians thought that Mondale was laying it on a bit thick, they were nevertheless pleased.

For in contrast to years of tension, especially during the Nixon administrations, the warm praise symbolized an end to old quarrels and a renewed climate of cordiality and cooperation between Canada and the United States.

Officials on both sides say that over the past year both governments have shifted their position. Thomas Enders, the U.S. ambassador here since early 1976, attributes "great changes" in Canadian attitudes to the Carter administration's display of understanding for its northern neighbor.

The frequency of high-level exchange visits between Ottawa and Washington indeed has increased dramatically during the past 12 months. Trudeau had met twice with President Carter and the two men are said to have hit it off well from the start. The new mood has produced tangible results, especially in the economic field.

But analysts of U.S.-Canadian relations tend to attribute the new warmth to a changing perspective in Ottawa caused by political and economic difficulties plaguing Canada.

The economic slump of the Canadian economy has been severe. Althrough Canada has reduced rampant inflation during the past two years, the current inflation figure is still hovering around 9.5 per cent annually; the unemployment rate for January stands at 8.5 per cent; and the Canadian dollar has slipped during the past three months by about 12 per cent against the U.S. dollar.

Far more important is a climate of political uncertainty caused by the secessionist movement in French-speaking Quebec and the threat it appears to pose to the integrity of the 110-year-old federation.

Since the secessionist forces led by Premier Rene Levesque have taken over Quebec's provincial government a year ago, most English-speaking Canadians have become virtually obsessed by the prospect of "balkanization."

Levesque has called for a referendum in Quebec next year to decide the provinces political sovereignty. But even the unlikely prospect that Levesque's forces could win a majority has produced a feeling of national crisis.

American officials in Washington say that there has been a substantial influx of Canadian funds into U.S. banks located along the Canadian border, especially into small banks in northern New York and Vermont. Also some small manufacturing and service firms have quietly moved south of the border.

What has intensified this feeling of crisis, however, are widely publicized moves of anglophone Canadian-controlled firms away from Quebec. A major political storm was touched off last week when Sun Life Assurance Co., Canada's largest insurance firm, announced intentions to move its corporate headquarters from Montreal to Toronto.

After Levesque charged that Sun Life's decision was aimed at "destabilizing" Quebec's economy, the federal government successfully persuaded the company to postpone its decision for two years.

Against this background of economics downtown and political uncertainty, the Canadians have gradually moved away from Trudeau's "third option" idea, the term he used for a set of policies that sought alternatives of Canada's dependence on U.S. markets.

"The third option is out," said a senior Canadian parliamentarian this week. "Nobody talks about it anymore." Also gone is much of the once-stinging Canadian rhetoric against "foreign domination," the term used by nationalists to decry U.S. economic investments in Canada.

Instead, the government has placed greater emphasis on expanding economic relations with the United States, with which Canada conducts two-thirds of its foreign trade.

What appears to be taking place, according to analysts of Canadian affairs, is a revival of the old concept of "continentalism," or merging of the two economies into a single North American unit.

A greater integration of the two economies, according to this view, offers both countries a way to expand trade and combat inflation and unemployment. It also provides Canada with what many Canadians see as an essential ally in their efforts to keep the country together.

The Carter administration has encouraged this trend by offering trade and tariff concessions while insisting that Ottawa be treated as an equal partner. Moreover, although the official U.S. position on the Quebec question is one of non-interference in Canada's internal affairs, the Americans have made it clear by implication that they favor a united Canada.