IN MR. CARTER'S State of the Union message, the sections inviting the closest reading are inevitably those dealing with Afghanistan and defense spending. In specific policy they go little beyond the administration's other recent pronouncements. But in tone and emphasis, they delcare that the search is now on for more effective responses to a challenge that, Mr. Carter says, is regrettably clear. It has been some time, for example, since you heard an American president promise a "significant" budget increase to improve the intelligence system.

The message is the first of the midwinter state papers by which a president tries to set his course for the coming year. Having sent this long printed text to Congress yesterday, Mr. Carter will deliver an abridged version himself in an address on Wednesday. Next week comes the budget, then the economic report. Together they will provide a fairly clear view of the general direction in which the administration hopes to go. But they will necessarily be short on precise descriptions of what comes next.

Administration policy over the coming year is very likely to be a response to two separate ranges of events. One has to do with Afghanistan, Iran, the Russians and the flow of oil from the Persian Gulf. The other is the much-predicted economic recession. The Afghan crisis is too recent for the White House to have developed fully its countermoves. As for the recession, the forecasts have been repeatedly wrong and that's why Mr. Carter has, quite propery, decided against cutting taxes. The economy has recently been showing itself to be expanding, to everyone's great surprise. But Mr. Carter knows that a recession could develop rapidly and, if it followed the pattern of the last one, a tax cut would be the correct and mandatory remedy. These uncertainties will unavoidably give this year's state papers a tentative and imprecise quality, in comparison with their predecessors.

But that's not altogether a bad thing. It means that national defense policy is changing, as it had to do. As for the economy, a cautious and pragmatic strategy is well suited to a moment in which no one really knows what's going to happen.

Beyond those two central subjects, this State of the Union message is remarkable mainly for the change of tense, from future to past, that comes toward the end of a presidential term. The document runs to 75 pages in its catalog of claimed accomplishments. Long sections sound very much like the party platform that the Democrats will adopt if Mr. Carter is renominated.

These messages are vulnerable to all the hazards that beset good intentions. Last year's message gave precedence to the ratification of the Strategic Arms Limitation Treaty and the enactment of hospital cost control. It promised a decline in the inflation rate. But inflation has gone higher than ever, and hospital cost controls still languish unpassed. Salt has, of course, been put aside. This year, Mr. Carter's message argues virgorously that Salt still serves this country's best interest. It will be high among his legislative priorities, he says, "when appropriate."