Three Navy men accused of spying for the Soviet Union represent the latest in an accelerating number of espionage cases that have snared Americans ranging from an FBI agent allegedly lured by money and sex to a California aerospace engineer who tried to sell Stealth bomber secrets to the Soviets.

In addition to retired Navy chief warrant officer John A. Walker Jr.; his brother, Arthur Walker, a retired Navy lieutenant commander; and his son Michael Walker, a seaman on the USS Nimitz, at least eight persons currently face charges of spying for the Soviet Union or Soviet bloc countries.

While there were no federal prosecutions for espionage between 1966 and 1975, there have been 37 cases since then, of which 27 involved the Soviet Union or its allies, Assistant Attorney General Stephen Trott said yesterday on the CBS television program "Face the Nation."

"Last year was our most productive year in terms of catching espionage activities," Trott said. "I believe, and the people with whom I've consulted believe, that there both is more espionage going on now, number one, and number two, we've gotten a lot better in detecting it."

Although Navy Secretary John F. Lehman Jr. is considering having John and Arthur Walker, both of the Norfolk area, recalled to active service and court-martialed rather than tried in a civilian court, "the case is going to be tried in federal court, not in military court," Trott said. Sailors in Norfolk react to Walker case. Page B1.

"We believe we can do that without compromising any of the secrets that are involved in this case," he said, vowing that the Walkers, if they are convicted or plead guilty, will not "get off light."

Law enforcement officials say they are convinced that the common denominator between the Walkers and others accused of espionage in recent years is the desire for financial gain.

"It says in the KGB manual, 'Americans can be bought,' " Bill Baker, assistant director of the FBI, said in an interview last week.

"It's a way to make money," Trott said.

That motivation differentiates modern-day spies from their counterparts in previous years, when ideological solidarity with the Soviet Union was a driving force for many accused of espionage.

"Most of the cases in the thirties and forties, those who spied for foreign powers did it for ideological reasons," former deputy CIA director Bobby Ray Inman said on "Face the Nation" yesterday. "I don't know of a single case in the last 15 years where ideology had a role at all. People are selling secrets for cash."

Now, however, "spies come in all different sizes, shapes, colors, backgrounds, philosophies and anybody who has access to this type of information, who has some sort of a strange personal situation going on, or a shaky financial situation going on, is liable to be this type of person," Trott said.

Among the reasons for the surge in espionage cases, government officials and other observers say, are the increase in the number of Soviets assigned to the United States, stepped-up enforcement and the growth in both the number of Americans cleared to see classified information and the amount of information deemed sensitive.

As restrictions eased during the era of detente, the number of Soviet nationals living legally in the United States has doubled during the last decade, according to Georgetown University professor Roy Godson, an expert on intelligence matters. Of those, a conservative estimate would be that 30 to 40 percent are working as intelligence officers, he said. "We are faced with a huge counterintelligence problem," Godson said.

Another unknown number of Soviet agents are in the country illegally, passing themselves off as Americans and, in addition to regular espionage activities, attempting to take such so-called "active measures" as influencing the media and governmental decisions, Godson said.

He cited the case of Col. Rudolph Albert Herrmann, a KGB agent exposed by the FBI in 1980, who spent 11 years collecting political intelligence and arranging secret exchanges of information with other Soviet intelligence operatives while posing as a free-lance photographer living in the New York City suburbs.

Sen. Patrick J. Leahy (D-Vt.), the ranking minority member on the Senate Intelligence Committee, has introduced a measure to limit the Soviet Union to the same number of individuals with diplomatic immunity here as the United States has in Moscow.

"I see no reason at all why we should allow them to have these large numbers of people . . . ," Leahy said. "We seem to bend over backward to do their job for them . . . "

Leahy also called for a reappraisal of the number of people with access to defense secrets. "We have 4 million people in this country with security clearances," he said. "That's crazy . . . People apply for security clearances, and 99 percent of them get it. I can't believe that that's showing enough care."

Another reason for the Soviets' apparent improved success in recruiting spies, observers said, is a perceived decline in feelings of patriotism.

"You've got the 'Me Generation' running rampant," said former CIA official George A. Carver Jr. "You've got the offspring of a generation which is not very ideologically motivated, which is extraordinarily self-oriented . . . which thinks, if the Soviets can supply their material needs, patriotism, honor, that means nothing."

One aspect of the Walker case that has officials particularly worried is that, although John Walker had allegedly been spying for the Soviets since 1968, the FBI was tipped off to the case only after a "walk-in" confidential source contacted them.

That differentiates the Walker case from most other recent charges of espionage. FBI officials were prompted to investigate Richard W. Miller, the first bureau member ever charged with espionage, after it started surveillance of Svetlana Ogorodnikova, a Soviet emigrant housewife, whose contacts with the Soviet consulate became frequent. Agents watching Ogorodnikova discovered that Miller had developed a personal relationship with the woman, who was working for the KGB, according to FBI officials.

The case against former Army counterintelligence specialist Richard Craig Smith, awaiting trial on charges of selling the Soviet Union information about American double agents, started when surveillance showed him in front of a Soviet compound in Tokyo.

And aerospace engineer Thomas Patrick Cavanagh, sentenced last month to life in prison for trying to sell Stealth bomber secrets to the Soviet Union, was snared when Soviet agents to whom he planned to sell information stolen from Northrop Corp. turned out to be FBI undercover agents.

"Some of the failures . . . to find out when this kind of stuff is going on is nothing more than a byproduct of the liberty that we enjoy in this country . . . ," Trott said. "One of the prices that you pay is that occasionally" somebody "will take advantage of it and become a spy.