Moscow is seeking to develop a radar-eluding cruise missile force, based at sea and targeted at United States territory, as a reply to planned deployment of new American missiles in Western Europe.
This, a senior Soviet official strongly suggested to the Monitor, is what President Leonid Brezhnev meant by his recent threat of an ''analogous'' response to the planned Western missile deployment. Some 600 new missiles, most of them cruise, are earmarked for basing in West Europe starting late next year.
Mr. Brezhnev coupled the warning with a call for a mutual ban on deploying ''sea-based or ground-based long-range cruise missiles'' - a leg of the arms race in which America has seized a considerable lead.
The official interviewed, a member of the Communist Party Central Committee, dismissed suggestions by some Western newspapers that the Brezhnev warning implied the basing of Soviet missiles in Cuba, a move that would violate a superpower understanding from the time of the 1962 Cuban missile crisis.
Another Central Committee member added: ''We are not idiots. There was an agreement in 1962, and we will fulfill that agreement.'' Western diplomats here report similar private assurances from the Soviets.
The diplomats say there is no indication the Soviets are within immediate reach of developing the kind of sea-based cruise missile tested by the US--essentially a small, pilotless aircraft designed for launching from a faraway point, hugging close to the ground on approach to its target, then delivering a nuclear charge.
Yet the Western envoys say they have little doubt Moscow is working hard on such a weapon and that they, too, have received private indications the Kremlin sees a sea-based cruise missile force as the best way of making good on President Brezhnev's threat.
The diplomats argue there are two key, unanswered questions about a Soviet bid for a credible sea-based force of cruise missiles:
* Precisely how far Moscow is from developing a long-range cruise weapon, as opposed to the much shorter-range, and relatively unsophisticated, cruise-type projectile the Soviet Navy already possesses?
* Will Soviet designers find an early match for the US cruise's guidance system, a dauntingly complex and miniaturized apparatus. ''This kind of miniaturized technology has traditionally given Soviet designers problems,'' a Western expert said.
The Soviet official interviewed, when asked whether the Brezhnev warning implied the basing of missiles in Cuba, replied: ''There are other ways, like the sea-based option, submarines, and particularly cruise missiles. It is known we are developing such a (sea-based cruise) weapon, too.''
Asked if Moscow envisaged basing such missiles on submarines, an option that would presuppose development of a longer-range Soviet cruise weapon, the official noted the cruise missile's size makes it a tough weapon for an enemy to keep track of. ''It can be deployed anywhere, even on a trawler'' near American shores.
He gave no details of how far the Soviets had progressed in developing a cruise missile comparable to the US weapon, but argued that a delay in agreeing on a cruise-missile ban would ensure a particularly dangerous new lap in the superpower arms race.
Comparing the cruise-missile balance to the superpowers' earlier development of multiple-warhead missiles, he said: ''Once the genie is out of the bottle, it's a lot harder to push it back in.''
Another Moscow official said only that past rounds of the arms race had demonstrated that ''if you (Americans) develop a particular weapon, we find a way to get something similar.''
Few US weapons seem to worry the Kremlin more than the long-range cruise missile. Articles in the Soviet press suggest this concern heightened with the expiration Dec. 31 of a protocol to the SALT II treaty limiting the range of sea-or land-based cruise missiles to roughly 360 miles.
Against this background, some Western analysts suspect Soviet officials may want to convey the impression their country is closer to development of a comparable cruise missile than is really the case.
Yet at least some of these analysts assume that sooner or later the Soviets will come up with a credible sea-based cruise force. The immediate question, one Western arms-control expert remarked, was whether the task would be accomplished sooner or later.