If Ronald Reagan is elected president Tuesday, he will be the first divorced man ever to win the office in America -- an irony worth a moment's reflection in the last days of this 1980 campaign.

For his entire political career, Regan has put himself on the side of the oldest verities of American public life. Without often dwelling on the specifics, he has successfully conveyed the impression that he will stand up for family, flag and old-fashioned goodness. This year he has taken the side of women who oppose a constitutional affirmation of sexual equality, and of Americans who regard abortion as "murder," a definition Reagan has embraced.

Yet as public acceptance of his own divorce suggests, Reagan has taken this position at a time when the values of American society are in great flux. Numerous polls have shown that tolerance of divorce, "living-in-sin," marijuana, pornography and homosexuality has grown enormously.

A Gallup Poll at the end of the 1960s, to cite one example, found that 85 percent of the public believed it should be illegal to send obscene material through the mails. But last year, when a Washington Post poll asked if it should be legal to sell pornography at local newsstands -- presumably a more controversial proposition -- the public split almost evenly.

Jimmy Carter, the first born-again Christian to occupy the White House, a strong family man whose famous youngest daughter is a highly visible member of the domestic first family, has never endorsed pornography or homosexuality. He, too, has sought to convey the impression that he believes in old-fashioned virtues.

But on specific social issues, Carter has aligned himself with the new tolerance. He actively supports the movement to liberate women from traditional family and career roles, embraces a Democratic Party platform plank opposing discrimination on the basis of "sexual orientation" and has rejected a legal ban on abortions, though he opposes abortion personally and favors the denial of federal funding for poor women's abortions.

The electoral consequences of the two candidtes' positions are not easily evaluated. Carter is apparently doing better among women voters, while Reagan is clearly the favorite of the relatively small number of activists who think abortion is the most important campaign issue. The ultimate voting choices of fundamentalist Christians might determine the outcome of the election, but polls suggest that neither candidate has a decisive advantage in this group of voters.

The practical consequences of a Carter or Reagan victory are equally difficult to assess in terms of these issues. The federal role in many of them is either constitutionally circumscribed or dependent on congressional action. The restoration of old-fashioned family values is probably beyond any president in an era when the most common size for an American family is two persons, and the old-fashioned family itself is an increasingly atypical phenonmenon.

But there is certainly a significant symbolic difference between Carter and Reagan that will reverberate through the society for the next four years, depending on which of them wins Tuesday. For as recent opinion polls indicate, the country really is divided between those who are sympathetic to the new tolerance and those who aren't.

If Carter wins, the political situation will likely remain much as it is, with the forces opposed to abortion, in favor of "family values," opposed to pornography and homosexuality fighting against a more liberal national government. But if Reagan wins, those same groups will claim credit for electing him, and can be expected to claim some of the spoils of victory.

And these could be some real spoils, as well as new impetus that a President Reagan could give to causes that have been around for some time. For example:

The "traditionalist" lobby has long sought to change the pattern of appointments to federal agencies and the federal bench. Reagan has publicly sympathized with this desire, embracing a Republican Party platform that called for appointing judges who respect "innocent human life" and lambasting judicial decisions that permitted legal abortions. During this time campaign Reagan has insisted that he will not demand that all his appointees share his views on abortion, however.

Reagan supports a constitutional amendment to outlaw all abortions, something Carter has opposed. So far, the movement behind such an amendement has failed to win substantial support in many states, but there is no sign that its supporters have become discouraged.

Reagan favors a constitutional amendment to permit voluntary prayer in public schools. According to his campaign headquarters, Reagan has not taken a position on the more immediate issue pending in Congress, which is a bill that would deny the Supreme Court jurisidiction over the school prayer issue. Passage of that bill -- which has attracted substantial congressional support already -- would eliminate the need for the more time-consuming process of amending the Constitution. Opponents of the bill have expected Carter to veto it if it were passed while he was president.

Reagan supports tax credits for private school tuition, a position backed by many church groups and staunchly opposed by Carter. On another education issue, Reagan has publicly expressed doubts about the validity of the theory of evolution, and indicated that he would favor that it be taught only as a theory, along with others like the biblical version of creation.

Early this year, in an interview with the Los Angeles Times, Reagan said he opposed allowing minors to get advice from a doctor on contraception without parental knowledge. That was "government sticking its nose into the family," Reagan said. But what if, Reagan was asked, "the family has broken down, what if the parents aren't there, what if it's a grandmother or aunt who's raising that child, and the child needs a contraceptive device or wants one, isn't it better to allow him or her to purchase it rather than to have an abortion or an unwanted baby?"

Reagan replied: "Whatever happened to just saying 'no'?"