A year in office, Ronald Reagan retains his split vision of national security. He believes in power--totally, unambiguously, sometimes simplistically. But he seems not to believe fully in government as the wielder of power: he shrinks from demanding military service from the young, from interrupting large areas of international commerce in the name of security, and more.

The public Reagan rhetoric leaves no doubt about his determination to do anti- Communist battle. Nor does his defense budget. He accomplished something of a political miracle in his first year by getting everybody--even their protectors-- to accept his premise that social programs, but not defense programs, had to be justified and had to be cut.

The personal Reagan image, however, is disconnected. He shows no awareness of a need to conform his personal life style at least a bit to the ostensible requirements of a state of national emergency. He appears insensitive to the widespread feeling that defense increases are coming disproportionately out of the pockets of the poor.

I was somewhat nonplused to learn that, though Reagan believes in tithing, he does most of his giving in personal donations not deductible from his income tax. Many people, I suspect, would be reluctant to have their personal welfare depend on an individual's discretion. Would Reagan be equally ready to have the nation's defense swing on a similar hinge?

In brief, the signals are crossed. One set tells the country, and the world, that the situation is serious and the United States means heavy business. Another set announces that the situation is not all that serious: private choices can still be enjoyed.

It is necessary to accumulate power and to use it to extend the realm of freedom to the citizens of other countries, Reagan is saying. But, he adds, in gathering and exercising that power there must be limitations on intruding upon the realm of freedom of American citizens.

Reagan still casts the impression of a Californian in Washington almost against his better judgment, a private man in a public job. You could see it in the palpable regret with which he said that, on account of the criticism, he would be switching some of his charitable donations into the visible deductible column next year.

At least until recently, the Reagan ambivalence seemed less noted at home than abroad. It is an essential reason, I surmise, why the Soviets have tended to discount the president's periodic declarations of ideological war and why they have waited to see what his real policy will come down to.

His ambivalence is also a reason why the Europeans have settled for half- measures, or quarter-measures, in Poland. Some of the Europeans' critics say the Europeans are merely using the American grain sales and non-draft to shield their own failings of will. Leadership, however, demands example, not just exhortation.

More recently, Reagan's ambivalence has begun to make a mark on the domestic scene. It has comforted some erstwhile critics, who find themselves pleased by any evidence of presidential moderation. It has set some erstwhile supporters to gnashing their teeth.

The lines may become even more confused in the next year. Given the president's reluctance to demand sacrifices from Americans across the board, he will have increasing trouble demanding sacrifices selectively, as he is now doing principally through social cuts. Abroad, meanwhile, he will have trouble demanding seemingly equal sacrifices for the Poles, since Europe depends much more on d,etente than the United States does.

Samuel P. Huntington of Harvard sees a contradiction arising from America's role in the world: to enhance liberty at home the power of the American government must be curbed, but to enhance liberty abroad it must be expanded. Huntington seems to feel it is mostly American liberals who are caught in this bind, but the Reagan case suggests that American conservatives--especially of the president's libertarian persuasion-- are caught in it, too.

This sort of contradiction disturbs some people. I hope not to lose sleep over it. I think our zigs and zags of the last 20 years are a pretty good argument for contradictions, or pressures, or whatever, that crowd policy toward the center. It will cost us some opportunities, but perhaps when all is said and done it will keep us on a straighter track.