THE TRACK RECORD of the man who is being sworn into office as the 40th president today induces a certain caution in the political analyst. Mr. Reagan has spent the past two decades beating the odds, defying the certainties and confounding both the assumptions and predictions of people who thought they knew what they were talking about. True, there were some elements of luck to it, but there always are. The fact is that Ronald Reagan, in an uncommonly straightforward and self-confident way, established his plausibility with a majority of the voters as a prospective president and as a preferable alternative to the president in power. That doesn't happen by chance or by fluke or even by the persistent foul-ups of the opposition.

So we begin with the fact that Mr. Reagan's election, like that of his predecessor in some respects, represents a distinctively personal triumph. They said it couldn't be done -- and it was. The good news since the election has been that Mr. Reagan does not seem even slightly disposed to exploit this personal triumph in the vain, vindictive or self-aggrandizing ways that traditionally have tempted those who win in this fashion. We do not mean to belittle the political and ideological meaning of the Reagan victory: the new president represented an unambiguously conservative Republican constituency and it is this constituency, this idea, that prevailed in the 1980 election. But, while staying faithful to the basic precepts with which he has enthusiastically identified himself over the years, Mr. Reagan has shown, it seems to us, an ease and openness and willingness to expand his perspective that is as admirable as it is essential -- essential to a successful presidency.

Mr. Reagan, some of his more high-pitched rightwing supporters to the contrary notwithstanding, is in no danger of becoming a liberal Democrat. If you don't believe that, just ask one. On a whole range of public issues he has remained a steadfast proponent of dismantling much of the handiwork of which the Democratic liberals were proudest. But he has insisted -- in the campaign and since -- that the inferences drawn by many of his opponents from the alternate policies he has espoused are wrong; he argues that his are not racially or socially or economically exclusionary programs, but rather programs intended to achieve the same unimpeachable goals as those espoused by his opponents -- only to do so in different (and better and more wholesome) ways. Similarly, he argues that his alteration -- toughening up, really -- of our foreign and defense policies is not a war-minded enterprise as charged, but rather a surer way to guarantee an honorable peace.

On the opposite page today, Rep. Jack Kemp sets forth his interpretation of the meaning of the Reagan election and the new administration's prospects for the next four years. His is a constructive vision. Whether or not you associate yourself with the particular economic theories associated with Mr. Kemp, in his commentary you see the broadest and most upbeat and positive understanding of what the Reagan administration is intended to achieve, what some of its most ardent and committed supporters expect of it. This is a day for good cheer. We hope the 40th president can achieve some large part of the happy vision that he and his associates are holding out to the American people.