On the day of his triumph President Reagan gave Lou Cannon a revealing interview in which he expressed all of the hope and all of the obtuseness that -- still -- seem to characterize his approach to international affairs. Far be it from me to say he should start working on the agenda of people who did not support him. But surely there are people with his ear who can tell him that if his remarks were an accurate preview of his second-term plans, he is on a risky, perhaps a doomed, course.

With customary earnestness the president declared that his first priority will be peace and disarmament. At the same time he put forward two familiar ideas that cut across the prospect of achieving even a modest measure of these thoroughly desirable goals.

The first of these ideas is that the Soviets will be forced by their relative industrial backwardness to accept an arms equation that otherwise they would not countenance. It is disconcerting that, with four full years in the White House under his belt, Reagan still does this matter straight.

Yes, Moscow feels an economic pinch, one that may well make it pine for the economic benefits, such as they might be, of arms control. But that is very different from indicating that to ease the pinch Moscow would accept a particular deal it felt was to its strategic disadvantage.

Reagan suggests that the Russians "will see the common sense value in (both of) us achieving a mutual deterrence at a lower level." What does he mean? Many reasonable people, believing that a rough parity existed when Reagan took office, would say that the Russians have long seen the value of deterrence at a lower level. It is Ronald Reagan who, arriving at the White House with the o-this-day-unproven notion that the United States was dangerously in strategic arrears, remains under a burden to show that he recognizes the value of deterrence -- equal deterrence -- at a lower level. Merely to talk soulfully about large reductions will not do.

The second idea Reagan offered was his "Star Wars" proposal for a defensive system to knock out Soviet missiles in space.

It's the only system for which a defense has never been created, the president said. But if that's true, it's meaningless, for you don't have to defend against a defensive system, you only have to evade or overwhelm it -- by general scientific testimony, not a difficult thing to do.

With such a system, Reagan went on, the Russians would finally have an incentive to reduce or eliminate their missiles, "since we've proven that it's possible to be invulnerable" to Soviet attack. But we have proven no such thing, and may never. In any case only someone who believes in Santa Claus would expect the Russians to sit on their hands for a decade or two while we worked up a system to render our deterrent invulnerable and to nullify theirs.

It seems awkward, at a moment of Reagan's political mastery, to be arguing rather technical points about one defense program. It is evident, however, that at this late date and as the president sets his second-term course, he appears oblivious to the poor fit of his Star Wars proposal with his grandiose hopes for disarmament and peace.

Are his friends on the inside telling him? In recent speeches, Secretary of State George Shultz has made the moderates' pitch. He described the Reagan strategic buildup as something already essentially consummated, his unstated implication being that Star Wars is not necessary -- although Kenneth Adelman, strangely for an arms control director, thinks it is.

Tackling administration hard-liners head on, Shultz said: ". . . we reject the view that we should become strong so that we need not negotiate. Our premise is that we should become strong so that we are able to negotiate. Nor do we agree with the view that negotiated outcomes can only sap our strength or lead to an outcome in which we will be the loser." Right on.

The evidence of Reagan's Election Day interview, however, is that Shultz, who has been on the defensive from the start, is still fighting an uncertain uphill battle for the mind and the attention of the president. If this is so, it may not matter that the Russians appear ready to resume some sort of strategic dialogue. Reagan will have put himself in a position to negotiate, and kicked it away.