In 1962 Mr. Trudeau asserted that the search for a separate Quebec state was a vain, negative and reactionary enterprise and that if intellectuals worked instead for the fruitful coexistence of the French and the English, Canada could be an example to the world.

In 1965 Mr. Trudeau entered federal politics largely to keep Quebec part of Canada, and 16 years later, in what is expected to be one of his last political battles, he is attempting to forge the basis for a new constitution. As part of the plan before Parliament he is proposing a bill of rights that would protect the language rights of the English-speaking minority in Quebec and the French-speaking minority elsewhere.

With five other provinces, Quebec has declared its opposition to the proposals largely because they do not respond to its principal concern: more autonomy. In the view of the province, the proposals even diminish its powers by limiting its ability to legislate in favor of the French language. Government Badly Defeated

The Quebec government, despite the backing of the leading intellectual lights of the province, was badly defeated last May when it asked voters in a referendum to give it the authority to negotiate sovereignty. Mr. Trudeau, who campaigned strongly for a no vote, is given some of the credit for that defeat.

In the Montreal speech in November Mr. Trudeau said an interviewer had asked him if he was not embarrassed to find himself opposed to the intellectuals. He said, ''It was sufficiently consoling to me to know that the population was with us and that it was, rather, the intellectuals and the artists who ought to be embarrassed that this people they presume to direct and sing about was completely opposed to their pro-independence views.''