Testimony by a high-ranking FBI official in a civil suit here indicates that the bureau may have many more people providing information to it on suspected American dissidents than William H. Webster, the new FBI director, asserted last week.

Associate FBI Director James B. Adams, in a sworn deposition in U.S. District Court here, testified in March that parts of the bureau's domestic security intelligence operation were renamed more than a year ago, although their basic function of furnishing information on American citizens was not changed.

Declaring that "we are out of the business of investigating organizations simply because they say things that are unpopular in this country," Webster said Wednesday in a speech before the American Newspaper Publishers Association in Atlanta that the FBI now has only 42 "domestic security informants." That is less than 8 percent of the 535 who, according to a recently released sworn statement by the FBI, were working in 1976.

However, Adams acknowledged at the March Chicago hearing that the FBI still has a nationwide network of people who never were classified as "informants" but who provide domestic security information to the bureau. As recently as 1975 there were more than 1,300 such individuals, and Adams said the number still might be that high, but "it doesn't appear to be."

These people formerly were designated as "confidential sources" but now have no formal designation, according to Adams. In FBI jargon, an "informant" is someone who takes an active role to gather information, such as infiltrating an organization, while a "confidential source" is omeone such as a college official or bank employe who merely passes along information gathered in the course of regular business.

Adams also said at the Chicago hearing that it is "possible" that one-fourth or more of the 535 informants active two years ago are still reporting to the FBI but are no longer classified as working in the domestic security area. These informants, he said, are assigned to such organizations as the Communist Party-U.S.A. and have been reclassified as "foreign counterintelligence assets."

Other informants may have been similarly reclassified, Adams said, but it would have been a "rare occurrence."

In April 1976, the attorney general's office tightened restrictions on FBI domestic security investigations in the face of accusations that the bureau had conducted widespread illegal wiretaps and burglaries against suspected American dissidents.

However, guidelines on investigations against those suspected of participating in foreign intelligence cases, if they exist, are classified. Also classified are the number of agents and informants engaged in foreign counterintelligence operations.

In the Atlanta speech, Webster said there are 1,789 informants reporting on general crime activities and 1,060 reporting on organized crime, in addition to the 42 domestic security informants.

Webster mentioned neither the current activities of persons formerly classified as confidential sources nor the extent of operations reclassified from domestic security to foreign counterintelligence.

An FBI spokesman said last week that a comparison of Webster's numbers with those of Adams was invalid because the reclassification had so complicated the figures that an analysis of them was "like comparing apples and oranges."

Adams' Chicago deposition was taken in connection with a class-action suit filed by the American Civil Liberties Union and other groups who allege their civil rights were violated by the FBI's domestic security activities.

An FBI spokesman said last week that neither Webster nor Adams was available for comment. The spokesman said he could not comment further because he had not seen Adams' deposition.