Federal Bureau of Investigation Director William H. Webster said yesterday that he has no plans to increase FBI surveillance of U.S. citizens, even though four have been arrested for espionage activities in the last three weeks.

"In a free society, this is the only way we can function without turning into a police state," he said. "Our focus . . . must be on the [foreign] intelligence operatives themselves."

Webster said the government should improve its security-clearance processes and reduce the number of classified documents and the employes who have access to them.

"There are too many classified documents and too many people -- more than 4 million -- with access to classified information," he said.

Included in the recent rash of espionage-related cases are those of Navy intelligence analyst Jonathan Jay Pollard and his wife, Anne Henderson-Pollard, accused of selling highly classified information to Israel; Larry Wu-Tai Chin, a retired Central Intelligence Agency analyst charged with spying for China for 30 years, and Ronald William Pelton, a former National Security Agency employe charged with selling secrets to the Soviet Union.

Webster said that these cases show "penetration or betrayal in each of our intelligence agencies . . . . The threat is real."

Speaking to the National Press Club, Webster said that the FBI does not have enough foreign counterintelligence agents to maintain surveillance of suspected spies from the Soviet Union and other hostile communist countries. The number of counterintelligence agents is classified.

Webster said there are more than 4,000 diplomatic and commercial officials from communist countries in the United States, about 2,500 of them Soviets. Based on the bureau's experience, he said, about one-third of those officials "are affiliated with intelligence services in their home countries."

In addition, he said, there are spies among the 15,000 students and 90,000 visitors who come to the United States each year from communist countries.

Webster said that the Soviets are becoming more aggressive in their spying activities, and have "an insatiable thirst for high technology" information and equipment.

The only common denominator in the cases of the Americans spying for foreign countries, Webster said, is money.

In addition, Webster said, some Americans become involved in espionage to avenge themselves on a former employer or to seek excitement.