Moscow — In dribs and drabs, Moscow is leaking details of its bid to create a huge ''modular'' complex in space. The space center, like the United States shuttle program, would carry clear military implications. Yet Moscow insists the aim is purely peaceful, and has called on the US jointly to ban space militarization.
The space complex could accommodate rotating crews of up to 12 cosmonauts, drawing on Moscow's already sizable lead in experience with lengthy manned missions. The complex's size would vary depending on how many units were added to the nucleus - a 45-foot-long cylindrical craft called Salyut first launched in 1971.
The first breakthrough in moves to expand Salyut by adding modules occurred in 1981 with the launch of a ''prototype module,'' dubbed Cosmos 1267, and its docking with the Soviets' sixth Salyut craft. After tests in which Cosmos's engines were used to steer the expanded craft, both Cosmos and Salyut headed earthward for prearranged burn-up.
Step 2 in the space complex program involves the recent launch of a second, larger module called Cosmos 1443 and its docking to the seventh Salyut.
Both the new Cosmos and the latest Salyut, emerging reports say, have been updated with assembly of a space complex in mind.
Salyut 7 includes a stronger docking mechanism to accommodate Cosmos 1443. The linkup of the earlier Cosmos with Salyut 6 had required a special adaptor.
The new Cosmos is about as large as Salyut itself, similarly shaped, and has been updated to include a ''descent'' module to tote experimental equipment, photographs, and the like for a ''soft landing'' back on Earth. The descent module separated from Salyut 7 Aug. 14, but its landing has not yet been announced.
The other part of Cosmos 1443 also was uncoupled for Salyut, carrying, among other things, space garbage. Presumably it will burn up in the atmosphere but this, too, has yet to be reported.
Western experts' attention, meanwhile, is focused on precisely what kind of craft the new Cosmos is, and on precisely what functions it is expected to perform. Though a complete picture still has not emerged, Soviet newspapers, television, and radio have provided considerable hints.
For one thing, the Cosmos can tote up to three tons of cargo to Salyut, much more than the workhorse Progress supply crafts routinely docked to Salyut since the early 1970s.
Beyond this, the Cosmos carries its own energy and life-support sources - thus already ''adding a room'' to cosmonauts' space environment when docked to Salyut, Soviet reports say. The Cosmos's independent engines are used to redirect the expanded Salyut-Cosmos craft.
This is no easy task since Cosmos-Salyut, plus the docked capsule that brought its two-man crew, already weighs some 50 tons. When Cosmos 1443 undocked , the capsule that had ferried the crew switched from one of Salyut's docking ports to the other partly to reestablish the combined craft's balance.
One recent Soviet report, meanwhile, hints Cosmos is not the final word in Soviet space modules, and might be used to manipulate differently designed units to and from Salyut. Moscow Radio aired a dialogue between a reporter and the designer of Cosmos 1443:
Designer: ''One should of course mention its function as a powerful interorbital tug.''
Reporter: ''. . . This means, let us say, certain modules could be moved to a lower orbit and then, using the same Cosmos 1443-type craft, they will be hauled up, as it were, to the orbital station, docked, and so on?''
Designer: ''This is a quite realistic picture, which this craft is quite capable of performing. This is no fantasy at all. This is reality, this is the tomorrow of our space exploration. Because in fact, as is known both here and abroad, the module principle of construction of space structures is accepted as being the one with the best prospects.''
This and other reports fail to reveal whether additional modules can be added to Cosmos while it is docked to Salyut.
The descent module of the current Cosmos was to parachute to Earth, but there has been no sign in the Soviet media that it is reusable.
The fate of the other half of Cosmos remains equally unclear - it could conceivably stay aloft even after undocking from Salyut 7 - but the Soviet press has said this portion will not return to Earth.
Seemingly more certain, for the time being, is that there is little prospect of a joint superpower ban on space militarization.
The US senses that Moscow classes the shuttle as a ''military'' vehicle to be covered by such a treaty. The Americans also allege Moscow has a lead in one important facet of space armaments - antisatellite weaponry - and seem determined to catch up before seriously weighing a space pact.
The US also worries about treaty verification. A 1981 Soviet proposal included widened verification provisions going some distance toward meeting that concern.
But the draft of a specific antisatellite ban suggested last week by Soviet leader Yuri Andropov and published in Pravda Aug. 22 omits this verification clause.