MR. CARTER did the right thing in assembling a panel of old national-security hands, led by the politically acute Clark Clifford, to help him decide how to handle the peculiar crisis that has arisen out of Cuba. The president is bound to draw more public support for his policy, whatever it turns out to be, if it is understood that he reached well beyond his own administration to arrive at it. It is a difficult moment for the country; it is the most difficult moment of the Carter presidency. The president needs the surest advice he can get, and he needs to be seen getting it and acting on it.

It is tempting to offer specific prescriptions for Mr. Carter to follow to get out of this fix, but he will reveal his own soon enough, on Monday, and it may be more useful at this point to try to define the kind of fix he is in. It is for Jimmy Carter a crisis of personal leadership, but it is also an authentic national trial -- not so much of "toughness," as some would have it, but rather of steadiness. And even those (we are among them) who feel it was produced in good measure by the administration's own ineptitude must care about the outcome. Questioning the president's competence or his policy-making process or his intelligence apparatus may be justified on the merits and will no doubt enliven the presidential campaign, but it serves no useful purpose now and should wait.

Some Americans point to the apparently uncontroverted fact that Soviet troops have been in Cuba unquestioned for years, and they think the president should do as the Kremlin and Fidel Castro demand: back off. But aside from what that would do to the president's political fortunes, it would be an unacceptable national humiliation. It would mean the certain demise of SALT, for one thing. Wisely or not, the president has committed the country's prestige to somehow altering the "status quo," whatever it was and is.Either by obtaining some modification of Soviet behavior or by taking some compensatory step of his own, he must act.

In acting, however, the president must be careful not to make the encounter larger than what he can effectively handle with the limited political and diplomatic resources he commands. This situation is still elastic; it has not yet been finally defined. If some would define it right off the screen and accept a cosmetic solution, others would make it a draw-the-line Soviet-American showdown and tempt a major confrontation. Both of these courses would be mistaken. There is a mean. Surely a steady, and steadied, president will find it.

What should be the objectives of such a policy? To bring more stability, not less, to the troubled Caribbean. To keep intact the possibility of measured judgments on SALT and on the size and shape of the defense budget. To demonstrate to all sides what most needs to be demonstrated: that the United States is capable of a sensible assessment of its own interests and of a sensible defense of them.