In stark contrast to American politics, Canada has a socialist third force whose political fortunes are on a marked upturn in the final days of the current election campaign.

There are no indications that Canada is ready for socialism or that Edward Broadbent, leader of the socialist New Democratic Party, would become prime minister.

But "Ed the Red," as the 43-year-old Broadbent jokingly refers to himself, seems likely to become a key power-broker if neither Pierre Trudeau's Liberals nor Joe Clark's Conservatives win a majority next Tuesday.

By becoming the balance of power between the two, the socialist leader could force policy concessions from either side as their price for his support.

Moreover, Broadbent's strategy to turn his party into a significant national political power has received a substantial boost as a result of his performance during Sunday's nationally televised debates with Trudeau and Clark.

The latest CBC polls shows the New Democrat with only 14.6 percent of the decided vote, against 40.9 percent for the Conservatives and 39.6 percent for the Liberals. But the sampling was carried out before the televised debate in which Broadbent made an impressive showing.

An affable former university professor who is a natty dresser, Broadbent has deliberately deemphasized socialist rhetoric since he became leader of the party four years ago.

The absence of traditional slogans in the current election campaign prompted a Conservative politician here, provincial Premier William Bennett, to quip that Broadbent was seeking to convey the impression that his Marxist doctrine was written by Groucho, not Karl.

Broadbent and his associates do not deny their socialist beliefs but they suggest that their political and ideological approach is similar to those of Scandanavian socialist parties.

Broadbent has persistently played up such nagging bread-and-butter issues as unemployment, high prices and weakened medical care programs. The central theme of his campaign is criticism of "foreign ownership" of Canadian resources, a veiled reference to the massive $50 billion in U.S. investments in Canada.

"It's time to bring Canada home to Canadians," Broadbent asserts at each rally. "Joe Trudeau and Pierre Clark - they are interchangeable - do not offer a real alternative.

"You give us 50 to 70 seats and we can turn the Liberals and Conservatives upside down, but if you give us the majority that I want, we can turn Canada right side up."

Broadbent expects the election to bring a significant increase in the number of New Democratic seats, from 17 in the 264-seat Parliament that was dissolved two months ago.

Broadbent advocates strong government intervention in economic fields.

Ideologically he is closer to Trudeau's Liberals but he has refused to say publicly what kind of concessions he would demand in exchange for supporting a Liberal minority government.

It is clear that Broadbent would insist on adoption of a part of his party's platform as official policy of any minority government.

By building a broader coalition that includes not only the Canadian Labor Congress but also the young environmentalists and other special interest groups, Broadbent is now seen as having a unique opportunity to enhance his party's national standing.

Since Sunday night's debate, in which a socialist leader for the first time was placed at the same level with the leaders of the two established parties, Broadbent's aides have shifted the thrust of their commercials to reflect his debating success.

The new ads say that if Broadbent were the leader of either of the two established parties he would win by a landslide Tuesday and that if enough people set aside their traditional affiliations and "vote for the best man, Ed Broadbent would be the next prime minister of Canada."

Political observers believe that the upturn in New Democratic fortunes may hurt Conservatives. There has been so much voter dissatisfaction with Trudeau and such ambivalence toward Clark that a number of Canadian may vote for Broadbent as a protest.

The New Democratic Party grew out of the old Cooperataive Commonwealth Federation, a party founded by Christian Socialists on the prairies during the depression years in the 1930s.

The New Democratic Party was formed in 1961 when labor leaders and leftist intellectuals joined the Federation to form a socialist party. At one point in the early 1970s the party ran the provincal governments of Saskatchewan, British Columbia and Manitoba and its members in Parliament propped up the minority Trudeau government from 1970 to 1974.

Broadbent has indicated that in return for his support now he would insist on a partial restoration of the anti-inflation controls that expired last year, under which price increases could be rolled back but not wages.

But his clear aim is to turn the New Democratic Party, frequently regarded as a social conscience in Canadian politics rather than an effective force, into a major national political organization. CAPTION: Picture, Prime Minister Trudeau catches a Frisbee while awaiting a plane to Vancouver. UPI