Soviet policy in Central America is unclear

''The Soviets would do something (in a conflict over) Cuba,'' says a well-informed diplomat here. ''But would they do something over Nicaragua? Where does that issue stand in the hierarchy?''

''Well, that's still an open question.''

Kremlin-watchers here in Moscow are searching for answers to it, though, as the latest controversy over Soviet arms shipments to Nicaragua continues to boil.

So far, the Soviets - while giving abundant rhetorical support to Nicaragua's leaders and asserting the country's ''right'' to arm itself - have avoided saying what they will do in response to increased United States pressure against the Sandinista government.

And the reason, according to the diplomat, is that the Soviet Union may not have formulated a clear policy itself.

''Where do they stand?'' he asks. ''I'm not really sure they know themselves.''

Indeed, Soviet experts on Central America have refrained from enunciating any clear set of Soviet goals and objectives in Central America.

It has therefore been left to Western analysts to try to piece together a possible Soviet agenda in the region. Here are the main themes that emerge:

* To preoccupy the Reagan administration with the situation in Central America, forcing it to channel attention and resources there.

* To foster ill will between the United States and Latin American countries, attempting to portray the US as a meddlesome ''Yankee imperialist'' bent on using force, rather than negotiations, to assert its will in the region.

* To encourage the spread of ''world socialism'' in the region without devoting much of its own resources in the process.

For their part, the Russians hotly deny that they are ''stirring up trouble'' in Central America.

''I wish we could create problems . . . there. But that's nonsense,'' an official says.

Western analysts say, however, that the Soviets unquestionably want to keep the Sandinista government in power.

The Sandinistas are, says another Soviet official, ''pioneers in fighting for solution to social, economic, and political problems.''

But he also makes it quite clear that Soviet support for the Sandinistas has it limits.

The Soviet Union, he says, has no treaty obligations with Nicaragua, or with any other Central American country. (And, therefore, it has no formal obligation to supply arms or troops, or to intervene in any conflict.)

''It's our position that peoples and countries defend their national interest by themselves.''

But, he adds cryptically, ''We hope that Nicaragua has wide support from various sources.''

Indeed, some analysts here suspect that the Russians are quietly sanctioning arms shipments from a wide variety of sources - including Libya, Bulgaria, Czechoslovakia, and North Korea.

In fact, the most recent high-level visit to Moscow from a Nicaraguan official was a stopover by Defense Minister Humberto Ortega Saavedra, who was on his way to North Korea.

Analysts here say that arms shipments were the main topics under discussion in both countries.

But one analyst says the Soviets would be cautious about engineering any major new commitment of armaments to the region now, especially while so much attention is focused on the area.

''They want to avoid having Nicaragua become a stalking horse,'' he says.

Another reason, he speculates, is that the Soviets are not so sure about the bona fides of the Sandinistas - and vice versa.

''The Soviets,'' he says, ''are not willing to stick their hands out and have them chopped off.''

''I don't think the Soviets were prepared for Nicaragua,'' he concludes.

''I think when it happened, they were pleased . . . but they weren't totally prepared in terms of knowing what to do with the situation.''

''Now,'' he says, ''they've got to react very carefully.''