IN DETROIT Ronald Reagan moved a considerable way toward consolidating his patronage of a kind of intellectual revolution in American politics. We are not speaking here of his and his party's views on foreign policy and national defense -- views that are, by now, familiar in their substance and that were generally set forth in Detroit as though the mere statement of them would make them come true. For all that Mr. Reagan has emphasized security issures in his attacks on Jimmy Carter, the heavy part of his appeal to the American people lies in his fundamental critique of the Big Government concept that administrations of both parties have supported since 1932. This seems to us the essential Reagan: to accept the legitimacy of the popular expectations raised by FDR but to vow to meet them by other than strictly federal means -- by the encouragement of free enterprise, the enlistment of popular energies, the devolution of powers to the state and local levels.

There is a problem here. Few people now claim that all it takes is new hands to make the system work better, or a little tinkering with the system itself. There is an evident consensus -- Mr. Carter had already felt it in 1976 -- in favor of rethinking the role that government plays in people's lives. This need not involve a mindless revocation of the services and benefits that, in the interval of four decades, have been built into the social system. It should involve as rigorous a review as the then-prevailing system received in the Great Depression. In Mr. Reagan's party, and elsewhere, there are serious people already going about this task. But in his party there are also unserious people who exult that their old slogans now look to be receiving a long-delayed political vogue but who do not see that those old formulas are, by themselves, a poor guide to public policy.

Here you come to the basic choices Mr. Reagan has to make now, which will be as important as the choice he made (finally, perils-of-Paulinewise) of a running mate. The convention in Detroit, its speechifying and its official documents, left pretty much open the exact way Mr. Reagan may take toward making good on the party's claims that it has something special and different and particularly apt to offer voters now. The Republicans profess, after all, to be rearranging their ancient values and ideas in ways that represent a serious and socially responsible challenge to the failed, prevailing liberal wisdom. But are they? And how will you know if they are.

The marvelously entertaining, if truly crazed, daylong Ford event, provides one clue. Mr. Reagan has sought and clearly wants and, to a large extent, has received the advice and support of the Republican respectables -- Cabinet members under President Ford and similar persons whose very working with him has gone a long way to eliminating the charge that his is a candidacy of the kooky right. But interestingly -- and wisely, if we may say so -- in the showdown hours of the Ford-for-Vice-President maneuvering, he finally rejected what had clearly become a bid by many in that government to seize and guide the Reagan effort, to make it nothing more than an extension of the Ford administration.

He was not captured by what we have come to think of as the 16th of July Movement. But his friendly association with so many of the figures from the Ford years does suggest that he also cannot and will not be swept away by the party's far right, those people whose interpretation of the convention's official pledges and its statements and silences is that the Detroit product vindicats the unreconstructed, ungenerous politics of resentment they themselves have long pursued. Mr. Reagan's acceptance address and the gloss put on the platform's meaning by some of its drafters, like Rep. Dave Stockman, and the overall pitch of people like Jack Kemp suggest that there is latent here anyway, the prospect of some new and important departures.

You don't have to love the idea (we don't) of the Kemp-Roth tax cut to see this. There is some evidence that important people in the party, and Mr. Kemp is one, are building an ideological rationale for an appeal to working-class voters and to other ostensibly Democratic constituencies that in not based on an attempt to exploit racial and social resentments -- anti-busing and the rest. It is based on a legitimate critique of the way government and government economic policy have been organized and the high cost that exacts from the citizen who doesn't have much to begin with.

There could be no better political news than that one of the country's major parties in fact had something new to say and might even be on the verge of nudging the tired and tiresome and irrelevant 50-year-old argument between the Democrats and Republicans toward something worth listening to. Most of the boilerplate coming off the podium at Detroit did not meet this standard. But we are optimists.