Adm. Hyman G. Rickover, boasting that he has not used the services of "think tanks" in 20 years, told a Senate subcommittee yesterday that all private consultants could be taken out "and drowned" and it would not make any difference in the way the government operates.

"They must be good for something," the feisty, 80-year-old admiral said of consultants, some of whom sat uncomfortably in the room during his subcommittee testimony. "Maybe they're good fathers -- but they shouldn't be good fathers at government expense."

Rickover's attack came during a hearing by the Senate Subcommittee on Civil Serivce and General Servces on a bill aimed at curbing abuses in the government's use of outside consultants.The proposed legislation would require federal agencies and private conultants to open up their contracting activities to more public scrutiny.

Though members of the National Council of Professional Services -- consultants all -- later came to the witness table to refute him, Rickover, director of Navy Nuclear Propulsion, fired some verbal torpedoes that clearly entertained the senators.

"It is all too easy for those charged with spending money that is not their own to be generous, particularly the government," said Rickover, who argued that the proposed bill should be substantially strngthened.

"Those in the consulting business are shrewd and have friends in government," Rickover concluded after citing examples of costly defense department studies. "These government employes themselves often look forward to acquiring the fruits of the consulting cornucopia, with the assistance of their friends in the racket."

While conceding later, under committee prodding, that his remarks did not apply to "all" consultants, Rickover said his experiences with them had seldom been good.

"I've had it happen," he complained. "They appoint outside consultants, and they have to be educated. And they have to find something wrong -- so they do."

He said studies had been done "in attempts to prove that non-nuclear aircraft carriers and cruisers are as effective as, but cheaper than, nuclear powered carriers and cruisers; that in response to the Soviet Union building faster submarines, we should build slower submarines . . ."

Rickover also accused former defense secretary Robert McNamara of hiring consultants to recommend that it would be "cost effective" to sink 10 Polaris submarines.

"McNamara was a systems man . . . he was off making speeches . . . but he had stooges there and we had a hell of a time."

Now head of the World Bank, McNamara was "climbing the Rockies" and could not be reached for comment, an aide said yesterday.

Rickover suggested that the best way to cut down on waste in the consulting business would be to reduce the funds available for such projects and to make them "more visible throughout the budget process."

Legislation to more closely regulate consulting activities was introduced last June following a series of articles in The Washington Post which detailed numerous abuses in the awarding of federal consulting contracts.

Sen. David Pryor (D-Ark.) chief sponsor of the bill and chairman of the subcommittee now considering its merits, opened the hearing by saying that outside consultants "do the basic work of government." And, while cameramen from the CBS television show "60 minutes" recorded highlights of the hearing, he and Sen. Charles Percy (R-III.) repeated many of the same concerns about contracting abuses they had expressed only the day before.

When the consultants got their turn, they complained that all the criticism of consultants had obscured their "extraordinary contributions" to the government.

"Yes, there certainly are some abuses -- and we feel the press and others have been very clever in taking advantage of anecdotal reports," said George Monroe, president of the National Council of Professional Services Firms.

But Monroe and other consultants argued that the goverment's overall procurement process should be streamlined. They said legislation aimed exclusively at curtailing consulting services could "eliminate a valuable and cost-effective resource."

Citing General Accounting Office reports issued between 1972 and 1978, Monroe said studies had found 16 government activities that were less expensive if performed "in-house" and 109 activities that were less expensive if done by an outside contractor.

Monroe recommended strengthening the Office of Federal Procurement Policy and upgrading the role of procurement officers within the goverment. He also said that waste would be avoided and services improved if the government paid private contractors promptly and if federal agencies had a better idea of what they wanted.

"It is very demoralizing when you put in what you feel is a good effort and come out with a valid finding and then find out the government is no longer interested," Monroe said.