IF ONE WISHED to be slightly malicious, the question one would ask of all our right-center presidential candidates is why they are ducking the other great issue of deregulation -- the government regulation of private social behavior.

None of them talks about that one -- about cops chasing marijuana smokers, legal barriers against homosexuals, divorce, pornography -- though it is as much a part of our times as its twin, government regulation of private economic behavior. Why shouldn't government, leave these private matters to the great marketplace of personal choice, just as it is being urged to let the marketplace set the price of oil? Can you envision a bumper sticker that says: "Decontrol Smut"?

Libertarians and anarchists are consistent on this -- they want the government to get out of everything -- but not most politicians. Ten years ago, many of them rallied against the aberrant behavior, the freaks in the streets, the unmarried couples living together, but today they are mostly silent on these matters. Let me suggest a radical explanation for this: In the last 10 or 15 years, without much leadership from the so-called leaders, America has become a much more tolerant society. This just plain happened, for diverse social reasons that lie far beyond the control of government.

This change in social attitudes is documented, again and again, in the best and only measurement available, the scientific samplings of public opinion, but it is rarely discussed in daily newspapers or other political forums. The absence of combat and contention makes for limp headlines. Try this one, for instance: "Americans Ambivalent on Legal Dope." Or: "Public Mellows on Porno Busts." Too mushy.

A decade ago, when America was in fractious turmoil on several fronts simultaneously, war, race, drugs, crime and weird social behavior, the politicians were advised to stand tall on the "Social Issue," which meant a vague collection of all these fearful phenomena. Get some distance from those long-haired freaks in the streeets. Defend the traditional values, hug the center, keep your hair trimmed neat.

In the short run, it was sound tactical advice. But politicians like Spiro Agnew tended to overstate the case and turn orthodoxy into a Sinclair Lewis caricature. Everyone can smile now at the memory of this certified crook playing the righteous preacher of mainstream values. On the other side, however, the failed candidacy of George McGovern in 1972 seemed to confirm the political lunacy of recruiting foot soldiers from among the freaks.

One of the central texts of that era was "The Real Majority" by Richard Scammon and Ben Wattenberg, a book on baseline politics that served as a brilliant corrective to the silly talk about a revolution in American values. At the center of the electorate, as Scammon and Wattenberg neatly reminded us, is a middle-aged housewife in Dayton, Ohio, and she doesn't like all this crazy new stuff. In fact, it frightens her. Politicians, the authors warned, had best speak to her fears because the center is where national elections are won or lost, not on the freak fringes.

Yet the Sammon-Wattenberg book and others that imitated it were remarkably simple-minded about what was happening in America. These sermons on the Social Issue failed to acknowledge that the center was moving -- moving rapidly in historical terms -- toward accepting the very attitudes that were supposedly so threatening. Re-reading "The Real Majority," I had the feeling that most of its prescriptions for winning rhetoric were not right or wrong today, merely irrelevant to the changed situation.

Yes, part of what happened was the end of divisive events -- the war in Vietnam, the racial explosions in American cities, the visible combat of social conflict. But something else happened, too. That legendary housewife in Dayton changed her mind about some thins. She discovered a stash of marijuana in her son's bedroom. She would never smoke dope herself, but her younger sister does. Her husband, after the war was over, grew a moustache and mutton-chop sideburns, and she likes him like that. Her daughter went off to college and -- horror of horrors -- chose to live in a coed dorm. The housewife from Dayton decided, on reflection, that her daughter was still her daughter and that some of this new behavior wasn't so frightening after all. Some of it made sense.

In short, the center of American politics -- that complicated mix of mainstream attitudes and opinions -- was gradually, undramatically, almost imperceptibly beginning to accept the unacceptable. Not because politicians told people to do so, but because people saw these changes in their own lives and neighborhoods and concluded, on experience, that they were not as threatening as they once supposed. Night after night, they also saw some of these strange things in their own living rooms, via the TV, and if TV programmers were putting formerly taboo scenes on the air, you could bet they were not disturbing to the Dayton bridge club.

In crude political terms, the opinion polls show that Americans are much more "liberal" today about divorce, pornography, dope, homosexuals, sex outside marriage, working women, abortion. But "liberal" is the wrong word. A better word is "tolerant." Most Americans do not watch filthy movies or smoke the devil weed, and most mothers and fathers do not want their children to do so either. But they are much less uptight today about other people who do it.

For example, a Gallup Poll cited by Scammon and Wattenberg found that 85 percent of the public felt a decade ago that it should be illegal to send obscene literature through the mails. This month, a new survey by The Washington Post asked voters about a much more public transaction -- the legality of selling pornography at local newsstands. The new survey found the people split almost down the middle -- 44 percent thought it was okay and 51 percent objected.

Not many years ago, the public was nearly unanimous on the question of allowing homosexuals to teach in schools. Now, according to the Post survey, the public is divided -- 40 percent have no objection and 51 percent are still opposed.

As one might expect, the traditional viewpoint is strongest among older citizens, though the new attitudes have permeated all age groups. As the young get older, carrying these more tolerant views with them, we can safely anticipate that the society will continue to change in that direction.

Politicians on all sides can smell a no-win situation, and with the public so divided today on these questions of social behavior, there's really no profit in coming down too hard on one side or the other. That's why, with the exception of abortion and occasional localized fights on other issues, we don't hear the kind of sweeping social rhetoric that Agnew made famous. An ambivalent public chooses ambivalent politicians.

The Post survey took a nice snapshot of the divergent social viewpoints with this broad question on social change:

"Many people seem to be doing things these days that would have shocked their families and friends 15 or 20 years ago. I am talking about men and women living together without being married, coed dormitories in college, and things like that. Generally speaking, would you say such changes in lifestyle are a sign of increasing moral decay in America or a sign that Americans are being more tolerant?"

The response: 35 percent see "moral decay," but 53 percent see a more tolerant America.

George McGovern perceived the future more accurately that Spiro Agnew, but McGovern paid dearly for announcing the future prematurely. Perhaps, a decade from now, after American attitudes have changed still more, we will be ready for the other great debate on deregulation.