FBI Director William H. Webster, locked in a struggle with congressional investigators over access to files on FBI informers, yesterday ordered "a full-scale review" of how the bureau's 2,600 informers are being used.

After testifying before the Senate Judiciary Committee, Webster said he instituted the review so he could be "completely confident" that guidelines to prevent misuse of informers are being followed.

His refusal to permit Congress' auditing arm, the General Accounting Office, to examine the informer fies has developed into his first serious clash with Capitol Hill. Webster, who has repeatedly endorsed effective congressional scrutiny of the FBI, contends that giving outsiders access to the files would irreparably damage the bureau's pledge of confidentiality to its sources.

Rep. Don Edwards (D-Calif.), chairman of the House Judiciary subcommittee that requested the GAO audit, said Webster's review of informers "is a very worthwhile action, but it's an internal audit. It doesn't resolve the problem."

The controversy over access to the files has significance beyond its effect on the congressional relations of Webster, who has just completed his first year as FBI director. Congress is preparing to enact a charter for the bureau, which would be the organization's first comprehensive legislative mandate.

Webster disagreed with an assessment by the American Civil Liberties Union that the new charter would be meaningless unless the GAO had access to the informer files.

The internal audit, which will be conducted by the FBI's planning and inspection division, is to be completed in 30 days, Webster told reporters.

In his testimony, he disclosed that the FBI has denied access to the files to its parent agency, the Department of Justice, which had been requested to study the informer progrme by Sen. Edward M. Kennedy (D-Mass.), chairman of the Senate Judiciary Committee.

Webster said the FBI had lost more than 200 of its informers in general criminal, organized-crime and terrorist investigations, reducing the total to 2,600.

A major factor in the reduction is loss of confidence in the FBI's ability to maintain the secrecy of its informers, he said.

"I'm confident those files should not be reviewed by anyone outside the bureau," Webster said.

He said he wanted the review conducted without "alarming young [FBI] agents who have responsibility for developing informations."

Webster told reporters that he viewed concern over possible abuses in the use of informers as "an historic outgrowth of our having involvement in domestic intelligence."

"That program has been scrapped," he added.

He said that attacking the informer program now because of past abuses amounted to "using a sledge hammer to awat a gant and doing damage to effective law enforcement."