Only three years after he was elected to Parliament at age 33, Joe Clark became leader of Canada's Conservative Party in a move so unexpected that it was greeted with the headline "Joe Who?" in a major Toronto newspaper.

Now Clark, 39, appears to be close to winning the May 22 general election thus becoming Canada's youngest prime minister in history. And that newspaper's question is still dangling in the air without a clear answer.

It is not that Clark is poorly known in the country. Quite the contrary. After three years as leader of the [LINE ILLEGIBLE] looking ungainly frame produce instant recognition. He was repeatedly mobbed during rallies through southern Ontario towns the other day, squeezing the flesh and fighting off the crowds like some singing star. Partisan crowds enthusiastically listen to his message condemning "Big Government," and advocating fiscal restraint and the revival of the old virtues of sturdiness, self-reliance and frontier pioneer spirit of the men who had built Canada.

Yet even among his supporters there is a sense of ambivalence about Clark the man and Clark the politician. Some think he is too young, or too inexperienced because he never had a real job, was never tested in the market place. Others are puzzled by big single-minded pursuit of power that has been so low key yet so effective.

Clark's detractors argue that he is all style and no substance, that he has been "programmed" by a group of sharp Tory operatives who are out to win and are prepared to have him say almost anything to attract notes.

How else could anyone explain, they ask, Clark's recent announcement that he would move the Canadian Embassy from Tel Aviv to Jerusalem, a promise that appeared to be aimed at gaining support from large Jewish communities in Montreal and Toronto? There are other apparent election ploys such as Clark's appeals to the elderly, promises of tax easements for the middle class and pledges to aid rural communities.

But what underlies public concern - both hostile and sympathetic - is apprehension that the May 22 vote may be one of the 'most crucial decisions in the country's history and that the man who wants to replace prime Minister Pierre Trudeau remains an elutive figure who has yet to show his ability to run Canada.

For the next prime minister will care to deal with the crucial issue of Quebec, where the separatist government wants to take the French-speaking province out of Canada.

For nearly a decade, the great Canadian national unity debate was conducted by two French Canadians - Trudeau, who opposed a separate Quebec, and Quebec Premier Reve Levesabe, who wants it - while English Canada was largely silent. Should Clark set elected, the Quebec problem could become the problem also of English-speaking Canada.

While Clark has said he does not recognize the right of self-determination forQuebec residents because it would mean a breakup of Canada, he has not spelled out how he would forestall the threat of separation. But his election would introduce a new tone in the debate and perhaps accentuate differences between the English-speaking majority and French-speaking minority

A Quebec novelist, Victor-Levy Beaulieu, pointed up the cultural and political differences between the two Canadas when he wrote, "Joe Clark is the cultural incarnation of English Canada odorless, colorless, tasteless. Ren Levesque and Pierre Trudeau, on the other hand, each in his own way, are the incarnation of Quebec and its culture, of what is vibrant in it, deep, triumphant and is vibrant in it, deep, triumphant and prodigious."

Trudeau and Levesque have different visions that they are prepared to fight for with a vigor that is foreign to a man such as Clark, reared in the Anglo-Saxon tradition of politics as a game without deep ideological underpinnings.

So as the election nears and as it has become apparent that most Canadians are tired of Trudeau's 11-year tenure, Joe Clark, his instincts and beliefs, have become the overriding issue.

He is an almost classic story of the boy out of a small frontier town in Alberta who made 1. big, first in local politics and then in Ottawa.

Joseph Charles Clark was born on June 5, 1939, in the house his grand-father built in High River, Alberta, after founding a weekly newspaper, the High River Times in 1905. Joe's grandmother was a native of Bay City, Mich., and his father, Charles, was born in the same house and still lives there.

Joe (that is the name he has used since entering politics) lived in High River, accommunity small enough for everyone to know everyone else, until he was 18. He worked as a paper boy and a sports writer for his grand-father's paper.

Even then he was involved in politics and was elected president of the student council.

At the University of Alberta, he did political work, chauffeuring a candidate. He graduated there with average marks but failed French, which caused Georgetown University to reject his application for postgraduate studies Clark was attracted to the Washington university because he wanted to be in the U.S. capital and it was a major Catholic university (he is a Roman Catholic).

By contrast, Trudeau graduated from the University of Montreal, was accepted at Harvard where he got an MBA and went on to study at the London School of Economics and the Sorbonne.

Despondent being unable to get into Georgetown, Clark went to Europe where he worked for a few months as a stock clerk in Harrod's in London and traveled in France before returning to Vancouver to study law. He quit law school in 1964 and returned to the University of Alberita to study political science.

Clark's contemporaries recall his university days as a period of political and journalistic activity. No sowing of wild oats, no passions, no hobbies. At parties he was to be found in a corner drinking Coca Colas and talking politics.

If there was any diversion from politics - then and now - it is escapist literature and movies - mysteries, detective yarns and westerns.

"He was never young," one of his top assistants says privately. His political science professor, Grant Davey, who likes Clark, said he never considered him "a serious or committed student."

"Attending university appeared merely as one of the several devices to advance his political ambition, said Davey.

His friend and biographer David Humphreys recalls Clark going to a rock concert in London in 1970 to figure out why youth would not support anyone over 30, the age he had just reached.

Once he decided to go into politics, Clark mused recently, he was "shcoting for the top." But to be prime minister of Canada he had to learn French, and later he surprised Quebec residents with the quality and fluency of his French. His wife, Maureen McTeer, who was once a research assistant on his staff, is bilingual.

Once elected party leader, he was notably successful in reorganizing the traditionally fractious Tories by working harder than anyone else at the behind-the-scene maneuvering.

He is not preoccupted by substance or ideology except in a broad sense. His talent, he said, is to piece things together through a complex combination of bargaining, cajoling and concilation.

"I offer no visions, I'm not an extraordinary man so I know that I must depend on other people, organize them - manipulate them, if you will - to achieve my objectives."

Clark called Trudeau an extraordinary man, but said his style of politics is "confrontational." He said Trudeau's problem is that "his vision and rhetoric raised expectations beyond the point at which he could deliver."

While Trudeau is barely on speaking terms which the 10 provincial premiers (none of them is a Liberal), Clark boasts that seven premiers are members of the party and that his forte is "teamwork."

There is something more than a little disconcerting about a man who talks about his "ordinariness." He won the party leadership by deliberately making himself the second choice of most factions in the convention. He wanted to become a novelist but picked politics as "my second choice" once he concluded that he could not succeed as a writer.

Then there is his youth. People used to joke that when Clark enters the room. Conservatives do not know whether to stand up or send him out for coffee. But he has changed.

One senses talking with Clark almost two years after an earlier interview that there is more drive, far more steel, and far less inclination to be deflected than his boyish look and physical ungainliness suggest.

He is offering a distinct path to Canada in its search for an identity.

"This country is really not a nation in the national sense, and perhaps it never will become one," he said. "We have something else, the multiplicity of communities" which are joined together by a "broad geography and a federal government."

What Clark suggests is that Trudeau's drive for a common Canadian identity and bilingual culture has weakened the fabric of Canadian life. What Clark wants is a multiplicity of cultures with a federal government acting as a broker among them.

He says he has no intention to dismantling social programs already in place such as federal health and pension schemes. But he says he wants economic programs generally favored by the conservatives and a smaller government more responsive to communities.

His program seems an appeal to the middle class: he would introduce deductability of mortgage interest and property taxer for homeowners; exempt capital gains tax on Canadian-owned companies' stock; encourage small businesses through special tax credits: and direct government purchases away from large firms to small and medium-sized companies.

Much of what he says these days belongs to the Conservatives election strategy. Yet much is also a part of Joe Clark from High River. Perhaps, just perhaps, Clark may be able to work out an accomodation with Quebec residents more effectively than Trudeau.

Few people question Clark's honesty, diligence or integrity. Polls show him scoring high on these aspects of his personality, but low for decisiveness, wisdom and experience. What is questioned is how his frontier ideals of Canada mesh with today's world of technology, large corporations and government, feminism, Quebec nationalism and the rest.

Richard Gwynn, a prominent Canadian columnist, put it this way:

"Clark recognizes that while our immediate problem is the state of our economy, our permanent and fundamental problem, the answer to the question of why Canada should exist at all, is cultural. Although his own esthetic tastes are banal, Clark brings to the resolution of our problems a deeper understanding of and a deeper commitment to the culture of Canada than does Trudeau, the philospher-king. A plugger wo may surprise us yet."