IS IT TRUE, as Cuba charges, that the United States issued its new report on the presence of a Soviet ground-combat force in Cuba to embarrass Fidel Castro while he is hosting the summit of the world's nonaligned states? Probably not. The timing seems to have been simply a matter of American intelligence putting together the pieces at this time. In a way, that's a pity. It would have reflected well on the administration's alertness to political opportunity if it had in fact timed the release to the summit. For whatever it means to the United States, it should be of consuming interest to the guests of the ostensibly nonaligned Mr. Castro to hear his explanation of the intimacy of his military ties with the Soviet Union. At a moment when he is trying to wrest primacy in the nonaligned movement from Yugoslavia's venerable Marshall Tito, this is potent stuff.

Why has Moscow put combat troops into Cuba? One hypothesis is that under the terms of the deal by which Moscow began deploying Cuban soldiers in Africa a few years back, the Kremlin agreed to put its own men into Cuba to steady Mr. Castro on his home ground. Another is that the Soviets are laying the groundwork for post-Nicaragua muscle-flexing in and around the Caribbean. Whatever the reason, troops put in place for one purpose can stimulate policymakers to find others. And the uncontested fact remains that the Soviet Union, in defiance of well-known American sensitivities though not of formal accords, has secretly injected a new form of military power into a volatile region just off the American shore. What would have been the Soviet reaction if Jimmy Carter had sneaked 3,000 Marines into Iran? There is no call for panic, but prudence compels concern.

One must then ask why the State Department, in announcing the presence of an estimated "2,000 to 3,000 . . . armored, artillery and infantry elements," pronounced this force "no threat to the United States." The judgment seems premature and gratuitous. Not only does the intelligence community feel it has a good bit more to learn about the force's military dimensions and political design, but by clearing Moscow before Moscow has answered its queries as to what's going on, the State Department virtually invites a brushoff. The rationale for offering the Kremlin a clean bill of health before the "disease" is diagnosed is, no doubt, that SALT must be protected against political contamination. But it is notable that the Soviets did not reflect a similar anxiety either in building up the force or in authorizing the recent maneuvers whose predictable detection brought the matter to the current boil.

Whether to expect the Carter administration to do anything effective about this force is problematical. The establishment of the force arose from a set of Soviet attitudes and judgments not easily affected by an enfeebled president deep into his third year. The only certain thing is that the event contributes to the atmosphere in which fresh decisions on military planning, and on political leadership, will be made. Meanwhile, however, it would be foolish to heed the fevered appeals of some senators to suspend the SALT debate until Soviet soldiers depart Cuban soil. Soviet-American rivalry makes it more necessary, not less, to weigh the SALT II treaty with care.