In 1957, the director of the Purdue Youth Opinion Poll, which regularly surveyed young Americans from coast to coast, reported that the average high school student believed censorship was necessary to protect "the public against improper ideas." In other respects as well, teen-agers then were revealing how long it had been since the American Revolution.

Last year, curious to compare present-day youngsters with those of the 1950s, Stanley Elam, a longtime judicious analyst of schooling, polled high school seniors in 26 states representing all regions of the country. He measured their responses against a Purdue Youth Opinion Poll taken in 1951 of the Class of 1952. The results are somewhat disquieting.

On certain questions that get to the vulnerable core of the Bill of Rights, the minority of students willing to make it easier for the state to put away certain alleged criminals has increased since 1951. So have those who believe certain religions are undeserving of full First Amendment rights.

Or, as Elam put it in the January 1984 issue of Phi Delta Kappan: "It is more than a little disconcerting to find a larger percentage of the Class of 1984 than of the Class of 1952 willing to allow a police search without a warrant, to deny legal counsel to criminals and to accept restrictions on religious freedom. It is also discouraging to see so many youngsters uncertain of so many traditional freedoms. . . . Most of these uncertain youths will have the privilege of voting in a presidential election during the same year in which they graduate from high school. They ought to be more vitally aware of their heritage or freedom than they are."

Well, 6 percent fewer of today's high school seniors than in 1951 believe that the cops or the FBI "may sometimes be right in giving a man the 'third degree' to make him talk." Back then, 60 percent of the youngsters were all for slapping the prisoner silly. Now, only 54 percent are. Only?

Although Elam did not intend his survey to be part of the presidential contest, his results came to mind during the recent reports by pollsters on how the president has so captivated the young that even after the first debate, he was ahead of Mondale among the 18-to-24 segment of the electorate by at least 17 points, according to one poll, and by even wider margins according to others.

As Elam and other observers of high schools have noted, our common rights and liberties are not taught with enough passion and pertinency to leave much of a mark on the students. All the more reason a national political campaign might have made for a rather compelling forum for some of these matters of basic liberties. But not much of that has happened either.

It's doubtful, for instance, whether the legion of 18-to24- year-olds, or most other citizens for that matter, knows that one of the presidential candidates had a bold role in a landmark constitutional case concerning fundamental American fairness. Clarence Earl Gideon wrote a note to the Supreme Court from a Florida prison saying he had been wrongly put away for five years, on a breaking and entering charge, because he hadn't had the money to hire a lawyer to defend him. And when he'd asked for one, Gideon had been refused.

As his case neared the Supreme Court, the state of Florida tried to get attorneys general throughout the country to join in an amicus brief against Gideon and supporting the right of each state to decide its own rules of criminal procedure. The man who was then attorney general of Minnesota not only refused to oppose Gideon's claim that he was entitled to a lawyer, he helped rally a number of his counterparts in other states to sign an amicus brief on behalf of the insistent convict. In 1963, Justice Hugo Black, writing for the Supreme Court, ruled in the Gideon case that anyone brought to court "who is too poor to hire a lawyer cannot be assured a fair trial unless counsel is provided for him."

Even if that story were told on national television by that former Minnesota attorney general, Walter Mondale, it probably would not have much appeal to the "I'm all right, Jack" generation. More likely to turn them on is federal appeals Judge Richard Posner, purportedly on Reagan's short list of possibilities for Supreme Court vacanies. Posner believes that cost efficiency is one dandy way of defining justice. For example -- as Lincoln Caplan has reported in this paper -- in the case of a prisoner who claimed the state was responsible for his blindness, Posner was against his getting free counsel, contending that the prisoner should see whether he could find a lawyer in the free market who might take the blind man on for a contingency fee.

Still, I'd like to see some campaign buttons mentioning Clarence Earl Gideon before it's too late. At least they would be collectors' items, maybe in more ways than one.