Two illegal flights of Soviet airliners over sensitive military and industrial centers in New England have called attention to the often fine line between Soviet civilian and military operations in the United States.
The episode is one in a string of attempts by the Soviet Union to use quasi-civilian operations as a front for gathering intelligence, says a prominent specialist on Soviet intelligence activities.
The incidents, recently disclosed by the Civil Aeronautics Board (CAB), also marked the second time in a month that the Soviets have been accused of illegal intelligence activities and have been forced to explain their actions. The overflights followed the grounding of a Soviet submarine inside Sweden's territorial waters, not far from a Swedish naval base at Karlskrona.
The Soviet government calls the incident ''a misunderstanding.'' But the CAB ordered a one-week suspension of Aeroflot flights as a penalty for the overflights.
On Nov. 8, one Washington-bound and one Moscow-bound Aeroflot airliner sliced overland paths above Massachusetts and Connecticut. They flew near a number of sensitive areas, including the US Navy submarine base at New London, Conn., and a General Dynamics shipyard at nearby Groton, Conn., where the new Trident submarines are being built.
A US-USSR treaty on commercial air travel requires Moscow-to-Washington flights to approach the US near the coast of Maine. They have to swing out over the Atlantic Ocean, skirting military bases and a band of defense-related industries in southern Connecticut. Flights then are supposed to cut inland over New York City and on to Dulles International Airport in Washington.
An article in the Armed Forces Journal last May describes attempts by the Soviets to fly over other ''sensitive'' areas in the East: Norfolk, Va., Philadelphia, and the Hudson Valley in New York.
Ralph Ostrich, senior strategic analyst with the Washington think tank BDM Corporation, says the overflights are the ''tip of the iceberg'' in a plan to intertwine intelligence activities with civilian airline and shipping operations of the Soviets and other Communist nations.
''That's not to say that we don't do the same thing ourselves,'' Mr. Ostrich says. The overflights ''are nothing to break diplomatic relations over,'' he adds. But the fact that they were exposed by the administration suggests a new bravado in dealing with Soviet intelligence activities.
''The Soviets have been wanting to do this for quite a while,'' explains Ostrich, who authored the May article ''Aeroflot: How Russia Uses Its 'Civilian' Airline for Covert Activities.''
''It's apparent (they) have been watching very carefully the situation with the air traffic controllers . . . and they slipped in a new (illegal) flight plan,'' he says.
The Federal Aviation Administration (FAA) says the Soviet pilots filed flight plans for the altered routes. But controllers along the route - perhaps inexperienced and unfamilar with the security restrictions - failed to challenge the plans. FAA monitors, which track aircraft from Communist countries, spotted the overflights on radar and reported them to the State Department.
The two aircraft were ''following the route(s) suggested to us by the Federal Aviation Administration,'' according to Soviet Embassy spokesman Michael Lysenko. The FAA, however, says it does not ''suggest'' air travel routes.
The official Soviet explanation given to the CAB: On the outbound flight, the Aeroflot employee filing the flight plan made ''an honest mistake.'' And the inbound flight, the Soviets say, was directed by Canadian air traffic controllers to take the overland route.
But a State Department spokeswoman says the overflights were ''definitely deliberate.''
''The Soviets have been doing this for a long time,'' says Ostrich. During the Carter administration the State Department ''looked the other way,'' he says , to avoid jeopardizing SALT negotiations. But Ostrich says his Pentagon sources have told him the Reagan administration decided to ''blow the whistle'' this time, part of the get-tough policy with the USSR.
Mr. Lysenko denies that there was any intelligence-gathering apparatus aboard the two aircraft. ''They were strictly passenger airlines on route from Washington, D.C., to Moscow,'' he said.
''There is no apparatus in the Soviet system which is not tied into their security system,'' says Ostrich. He notes that Aeroflot's director is also a marshall in the Soviet Air Force. Half of the Aeroflot fleet is military reserve aircraft (bomb bays removed), he says. They come complete with a glass nose from which the bombardier looks below.
Aeroflot planes provided a ''low profile'' with which to quietly unload troops into Prague in 1968 and Kabul, Afghanistan, in December 1980, according to Ostrich.
Officially, some US government spokesmen give the Soviet story the benefit of the doubt.
''They could have been showing their passengers what the US looks like for all we know,'' says a Navy official. Others suggest the aircraft were flying at too high an altitude to get a good glimpse of anything.