WASHINGTON (AP) _ The CIA and FBI ``significantly delayed the detection'' of CIA turncoat Aldrich Ames by failing for five years to mount a serious, joint investigation of their stunning loss of Russian agents in 1985-86, the Justice Department concluded Monday.

Justice Inspector General Michael Bromwich said a joint investigation did not begin until August 1991, which led to the 1994 arrest and guilty plea by Ames, the most damaging mole in CIA history. Bromwich released a brief summary of his top-secret 400-page report on the FBI's role in the case.

The FBI said it ``has strongly taken issue with many aspects of the report,'' adding that the study highlights relations between the CIA and FBI ``that have long since been improved and fixed.''

The FBI looked into its own losses in 1985-86 without finding an explanation, and took a passive view when it learned that CIA had lost even more agents during that two-year period, Bromwich said.

``The FBI ignored the obvious disaster at the CIA'' even though it is responsible for investigating foreign spying against the United States, Bromwich reported.

``The failure of the CIA and the FBI to pursue a joint investigation of the lost assets prior to 1991 significantly delayed the detection of Ames' espionage,'' Bromwich concluded.

Ames pleaded guilty to selling secrets to the Soviets for more than $2.5 million, beginning in 1985. He is blamed for the loss of at least a dozen Soviet and East Bloc officials spying for the West, including two officials in the Soviet Union's Washington embassy who were reporting to the FBI.

The pair, Valery Martinov and Sergei Mortorin, were abruptly recalled to Moscow in 1985 and executed in secret.

An FBI team looking into those losses had heard by early 1987 from the CIA ``that the CIA's Soviet program had rapidly suffered unprecedented losses of its most significant assets at the same time the FBI was experiencing its asset losses,'' Bromwich found. But the FBI team's September 1987 report failed to mention the CIA losses.

``The FBI Director and the Assistant Director in charge of the intelligence division never gained a true understanding of the scope and significance of the CIA's asset losses in 1985 and 1986,'' Bromwich wrote.

``Mid-level FBI supervisors and FBI line personnel appear to have believed that receipt of this information imposed no responsibility on the FBI.''

In an interview, Bromwich said: ``The lack of information flowing to higher-ups surprised us. The directors and assistant directors are responsible but they have to be given basic information.''

In May 1987, the FBI Director, William H. Webster, switched to the post of CIA Director. But that did not solve the problem.

Bromwich concluded that between September 1987 and mid-1991, ``the CIA must bear primary responsibility for the failure of investigators to focus on Ames.''

By late 1989, the CIA had learned that Ames, who had access to information about the lost agents and a salary of no more than $50,000, bought a $540,000 home for cash that year and had three large, unexplained cash transactions totalling more than $50,000 between 1985 and 1989.

This ``potentially incriminating information'' could have led to an FBI investigation of Ames, Bromwich wrote, but ``no information concerning Ames was provided to the FBI prior to mid-1991.''

Had it been, investigators might not have had to wait until the summer of 1992 to discover in U.S. records that Ames had meetings with a Soviet diplomat in 1985 and 1986 which were followed the next day by large cash deposits to Ames' bank account, Bromwich said.

Among a series of tighter counterespionage checks imposed since late 1993, the FBI noted that a senior FBI agent now heads the CIA's counterintelligence group. A senior CIA officer now is assigned to FBI headquarters.

The FBI said the new cooperation was reflected in the arrest and guilty plea earlier this year of former CIA station chief Harold J. Nicholson on charges of spying for Russia.