In the closing days of his campaign, Ronald Reagan would conduct a quiz with his crowds. "Are you better off than you were four years ago?" he would ask. "No," they would reply. "Is your family more stable than it was?" "No," came the answering shout.

It was a revealing exchange -- and one that is freighted with significance for the future of American politics. As William Safire of The New York Times has pointed out, there were two quite separate impulses reflected in the Reagan-Republican victory.

One was the widespread discontent with the economic policies of the Carter administration -- the burden of taxes, regulations and inflation that made the Reagan voters tell him, "No," they were not better off than they had been.

The other was the concern with drugs and divorce, with the changes in personal and family relations, social and sexual norms, morality and religion that made the Reagan crowds say, "No," they were not sanguine about their families' stability.

Those two impulses, reflected in those two questions, set two different agendas for the incoming administration. The economic mandate is to reduce government spendng, taxation and regulation and give people more room to seek their own goals. The social mandate is to expand the government's efforts to prescribe and regulate individual behavior. As described by the Rev. Jerry Falwell, spokesman for the Moral Majority, the agenda includes constitutional amendments to ban abortion and reinstitute school prayers, legislation to restrict pornography and drug use -- and opposition to the Equal Rights Amendment.

As I have visited a series of campuses, civic clubs and business forums in my post-election wanderings, what has been borne home to me is that Reagan and the Republicans face a fateful choice on which agenda they accept.

To put it as directly as possible, if they choose the economic agenda, they have a chance of success that can broaden their constituency and give them a leg up on the Democrats in the struggle for the future of American politics. If they choose the social agenda, they will squander their energies in what is probably a losing cause, divide their own ranks and alienate the very voters who could make them the majority party of the next three decades.

Those are sweeping and controversial statements, but the evidence that supports them is clear. There is very broad readiness -- at liberal universities as well as in industry meetings -- to see what Reagan and the Republicans can do for an ailing economy with their free-marker policies. But there is no such acceptance -- either in the dormitories or in the board rooms -- of a return to Prohibition-era efforts to legislate social behavior.

In the campaign, Reagan and other Republicans reaped votes from new constituencies of fundamentalist Protestants and Catholics by sympathizing with some of their social-issue concerns. Bt giving priority to that social agenda could carry substantial risks -- as George Bush has been saying -- of alienating the high-church Protestant voters who make up the Republican base. These are men and women whose celebration of their party's victory is tempered by their firm opposition to having the government dictate what they read, or think, or say -- or how and where their children pray.

If Reagan makes Falwell's crusade his personal cause, he will find himself expending energy and political capital that could otherwise be used to push his economic proposals.

And many of those who would fight him on the social agenda would be his own people.

It is possible -- though far from certain -- that Reagan has some answers to the economic woes of America. It is highly unlikely that he or any other president can "cure" the social ills of our time.

Jimmy Carter may be responsible, to some degree, for the resurgence of inflation, but the rise in the divorce rate, the emergence of homosexuals from the "closet" and the growing number of unmarried couples sharing domiciles are evidences of social changes far beyond the reach of any president or any democratic government.

Besides, there is no American consensus that the changes are as destructive as Falwell and his followers sincerely believe them to be. When The Washington Post Poll asked, a year ago, if divorce, cohabitation, coed dorms and other such phenomena were evidence of "moral decay" or "greater social tolerance," by a 3-to-2 margin, the cross section of Americans of ages answered "tolerance." Among those between 25 and 35, that was the answer by a 3-to-1 margin.

In that poll and others, less than one-third of that "baby-boom" generation expressed agreement with the Moral Majority's condemnation of the Equal Rights Amendment, cohabitation by unmarried couples, homosexuals teaching in school, easier divorce laws, open sale of pornography or use of marijuana.

Those young people between 25 and 35 are vitally important to our political future. They make up 36 million of our present voting-age population of 160 million, but most of them are on the sidelines of politics now, watching but not participatng in the elections.When they make their choice of candidates and parties -- as they undoubtedly will later in this decade -- they will put their stamp on the future of our politics.

Reagan has an opportunity to win their support by making the Republicans the part of prosperity. If he devotes himself, instead, to an effort to impose an older-generation view of morality on the younger generation of Americans, he would waste a historic opportunity -- and divide his own party in the process.