Quietly, deliberately, beyond the gaze of Western military attaches, the USSR has begun work on bridging the great Rubik Cube Gap.
While toying - pun not intended - with importing the Hungarian original, and while readying a late-September welcome in Armenia for inventor Erno Rubik, the Soviets have come up with the prototype of an officially proclaimed competitor.
It is called the Moldavian Pyramid. And a three-paragraph mention in Pravda has prompted a premature rush on Moscow toyshops. This is not surprising. Mr. Rubik's front-runner already commands a black-market price that, at official exchange rates, is comfortably above that of a share of General Motors stock. One American woman was recently offered 35 rubles, about $50, for a tiny, key-chain model of the cube.
Initially, senior saleswomen on the ground-floor toy area of Detsky Mir, the nation's largest children's store, declined comment on both cubes and pyramids. A small group of attendants in a far corner finally broke the silence.
''We've been getting loads of requests for the pyramids,'' said a pleasant young woman with close-cropped dark hair and an infectious smile. ''I'm afraid we don't have it yet. Perhaps you could come back after the new year.''
A somewhat older lady took up the conversation: ''There are rumors we're going to purchase the Rubik Cube, too. But who knows?''
Asked where to find the cube in the meantime, she grinned and ventured: ''Maybe Budapest.''
Fueling consumer interest in the cube has been a smattering of interviews with its inventor in Soviet newspapers. One, on New Year's Day this year, quoted him as saying: ''I (have) received thousands of letters from people who are interested in the cube but do not have it yet, including letters from the Soviet Union.''
Mr. Rubik added an enticing postscript: ''Incidentally, foreign trade organizations are currently conducting negotiations on distributing the game in your country as well. . . .''
Hungarian representatives here say unspecified problems have held up agreement so far, but add that Mr. Rubik and his cube will both be on hand for a Hungarian trade exhibition in the Soviet Armenian capital of Yerevan at the end of September. One Hungarian journalist says Yerevan's Communist youth newspaper has already conducted a written interview with Mr. Rubik to set the scene for that visit, and that ''maybe there will be some agreement on licensing'' about the time he arrives.
Meanwhile, at a factory in the frontier Soviet republic of Moldavia, work proceeds on the Soviet competitor. If the Moldavian Pyramid is anywhere near as complicated as Pravda's brief description of it, brains nationwide promise to be teased.
Yet the newspaper adds, reassuringly, ''The number of variants, though astronomical, is less than in Rubik's Cube.'' The idea is to arrange 14 small pyramids, in proper color sequence, to form a single larger one. The pyramids, Pravda explains, ''are moved around an axis opposed to one another at uneven angles.'' This correspondent will pass.
At another Moscow toyshop, a product supervisor says the pyramid should be off the production line some time early in 1983.
Her only concern is that, with demand likely to be enormous, the ''Moldavians will keep their pyramids for themselves.''