Defense Secretary Caspar W. Weinberger said yesterday that contract abuses by weapons manufacturers appear to be limited to "a few bad apples" and defended the industry as a national asset.

Weinberger warned, however, that the Defense Department will take "strong actions" to stop "particularly dishonest or inefficient or frankly stupid" practices by contractors, including billings to the government for frivolous overhead costs. He said he will move immediately to prosecute any firm that knowingly submits such claims.

In an interview aboard the airplane bringing him back from a NATO meeting in Luxembourg and a visit to France, Weinberger also said:

* European officials continue to fear that President Reagan's "Star Wars" missile defense will undercut the western strategy of deterrence, with the French voicing particular concern that a space-based missile defense system would render useless their independent nuclear force.

* Allies can take longer than the 60-day deadline he set in his formal invitation last week for European participation in Reagan's proposed $26 billion research for the Strategic Defense Initiative (SDI), a deadline some interpreted as an ultimatum.

* He has "no problem" with a joint European bid to cooperate in the research project.

On defense contractors, Weinberger sought to underline the "get tough" policy he announced a month ago when congressional critics blamed the Pentagon for tolerating runaway costs on weapons systems.

The controversy has been fanned in recent weeks by reports of contractors billing for such expenses as boarding an executive's dog and disguising part of the cost of a $748 pair of pliers as overhead expenses.

While he called those claims "very disturbing," Weinberger said they appear to be isolated cases and should not tarnish the image of the defense industry, which "provides the talents for what we need to regain our defense strength."

"I don't think a few bad apples in any sense should cause you to judge the whole barrel," he said. "The whole barrel is one of the things that helped us survive as a nation and it's one of the great advantages of our kind of system."

He pledged, however, to deal "very strongly and very immediately" to punish wayward contractors "whenever we find them, whether they're a pattern or not, whether they're one or two or 15 or 20. I certainly don't want to shrug my shoulders at something and say everybody does it. I don't think everybody does do it."

He said his new requirement that contractors sign an affidavit certifying that their claims are proper is a "structural change that in effect says don't submit these bad bills . . . . We're not going to hesitate to refer anybody for prosecution [of perjury] who seems to lie."

In his meetings with European defense officials, Weinberger said he was questioned whether "there was some imminence" to development of a "Star Wars" defense "and wouldn't that be a danger if we didn't succeed."

Weinberger said he assured them that any decision to deploy the space-based missile defense is years away and that the United States is committed to strengthening its deterrent capability by modernizing its nuclear force.

"We're not going to substitute something we have for something we need," he said.

As for French fears that a a missile defense system would neutralize their small nuclear force, he said, "We're not talking about anything that's going to render it useless tomorrow."