The Soviet Union may be conducting "an invasion by osmosis" in Poland with a "gradual filtering in" of additional troops, U.S. Defense Secretary Caspar W. Weinberger said today.

Since Moscow started its military maneuvers around Poland, it has been "very hard to tell whether there's going to be a conventional-type invasion or an invasion by osmosis," Weinberger added as he prepared to discuss the issue here with fellow defense ministers at a three-day meeting of the NATO nuclear planning group.

Either way, he added while deploring the continued high tempo of Warsaw Pact military movements in and around Poland, "The whole activity can't fail but be very intimidating and coercive, and I think that's exactly what its intent is.

"There's something that has been taking place here," continued Weinberger, "that is intended to have the same coercive effects on the Polish people as an invasion."

Weinberger's remarks were made earlier in the day on a trip to an air base in Cottesmore, England, and during the flight here.

When asked by reporters how many Soviet divisions already are within Poland, the defense secretary said he did not know the numbers.

Earlier in his trip, Weinberger stopped short of characterizing the Soviet military flights in and out of Poland in recent days as an airlift. He called it "rotation" of troops, which suggested that troops were leaving as well as entering Poland.

Weinberger said he does not expect NATO nations at the meeting here to draft a plan of action in response to the threat of a Soviet invasion of Poland.

Weinberger and John Nott, his British counterpart, discussed the Polish crisis while visiting the Royal Air Force Base at Cottesmore -- the home of the Spitfire bombers during the Battle of Britain in World War II. The military tour was designed to give Weinberger a close look at the new Tornado fighter-bomber being built as a joint NATO project by Britain, West Germany and Italy.

Pilots of the three NATO countries are being trained in Cottesmore to fly the Tornado, which carries two crew members and will be produced in versions to support troops and to engage in aerial dogfighting.

John Nunn, a Royal Air Force wing commander, said the radar of the Tornado, with a man in its back seat to study the blips, could outdo the U.S. F15 fighter plane, which carries only a pilot.

"I suspect we could shoot down the F15 before they could see us," Nunn quipped. He said the United States will not buy the Tornado, however, "because it wants to keep its factories busy."

NATO leaders long have complained that the United States has not made military procurement for the alliance a two-way street, selling far more weaponry to its allies than it is willing to buy.

"I've asked the secretary to buy 200 of them," said Nott jokingly to reporters as he stood alongside Weinberger.

"I've got the brochure," Weinberger replied with a smile.

The two defense officials flew together from Cottesmore to the Lakenheath Royal Air Force base in Suffolk on the North Sea where the U.S. Air Force has based 90 F111F fighter bombers, which have enough range to drop either conventional or nuclear bombs in Warsaw Pact countries. American nuclear-tipped cruise missiles also are scheduled to be based at Lakenheath in what Weinberger described as a countermeasure to the Soviet SS20 missiles targeted on West European nations.