FBI Director William H. Webster disclosed yesterday that his agency currently relies on 2,900 paid informers to help penetrate criminal activities across the nation.

Last year, he said, information supplied by such outsiders led to 2,600 federal arrests and the recovery of some $200 million of stolen merchandise.

Speaking to the annual meeting of the American Newspaper Publishers Association, Webster conceded that many people are uneasy about talk of informers. "But I have to say to you that the informant is the most effective tool in law enforcement today" at the state, local and federal levels, Webster said.

After his luncheon address, Webster said he had decided to speak out about the extent of FBI-informer relations because of a growing concern about the confidentiality of such sources, expressed by FBI field agents here and in other cities.

In his speech to more than 1,000 publishers and other newspaper executives, Webster said the FBI gets valuable information from tipsters, informers placed by the FBI in various groups and from the agency's own force of undercover agents, who are placed inside some organizations permanently so they can become part of leadership and reach the top of criminal operations - a more time consuming and costly process.

Of the outside informers, Webster said nearly 1,800 report on general criminal activities, 1,060 on organized crime and 42 are involved in national security cases. The last figure contrasts sharply with claims that thousands of FBI informers were involved in monitoring various organizations in the United States in recent decades. It is thought that this is the first time that the FBI has made these figures public.

Webster said later that practically all of the 42 national security informers are watching groups involved in potential terrorist activities. While the FBI no longer monitors organizations "simply because they say things unpopular in this country," Webster said the agency is currently watching 61 individuals and 12 organizations with "terrorist activities afoot."

Webster said he could not disclose information about foreign counterintelligence operations in the United States that may involve informers. However, he revealed, in 1977 the FBI paid $927,000 to informers for general crime information and $543,000 to informers engaged in watching organized crime.

In a slow, deliberate discussion of his agency's current state, Webster said the informers are monitored closely by field agents and FBI inspectors.He said the agency is careful to keep informers from "creating situations" and required them to behave as an FBI agent with no participation in violence or unlawful acts.