WASHINGTON (AP) _ The CIA publicly asserted Friday that turnabout defector Vitaly Yurchenko is a 25-year KGB veteran who most recently supervised Soviet spying in North America and has worked on putting double agents into U.S. intelligence services.

In an uncommon move, the CIA issued a three-page biography of Yurchenko, 49, listing all his spying posts and responsibilities. The document gave no indication of where the information was obtained or how it was verified.

CIA spokeswoman Patti Volz declined to comment on why the paper was released now. But the release came two days after critics inside the Reagan administration, in Congress and among retired CIA officers had begun to take the agency to task for its role in the Yurchenko affair and to suggest that he was not the top-level Soviet spymaster described by the State Department on Oct. 11.

Yurchenko himself stunned Washington by turning up Monday at a Soviet embassy news conference to say that, rather than the biggest defector in years, he was simply the victim of a kidnaping by unknown men in Rome.

He said he was brought to Washington unconscious and the CIA held him for three months against his will while they used torture, drugs and threatens to try to pry secrets out of him.

The CIA's document, however, repeated the U.S. version that he requested political asylum at the U.S. embassy in Rome on Aug. 1. It also revealed that ''his relationship with his wife was seriously strained prior to his defection.''

U.S. sources had described him in the subsequent three months as the KGB's No. 5 official, but this week one source told The Washington Post he was merely a colonel in a KGB department with numerous generals and probably wasn't even No. 50 in rank.

Another source suggested to The Washington Times that Yurchenko had been pictured with top KGB officials in the Soviet newspaper Pravda in June merely to give a false impression of his importance in order to set up a phony defection.

National Security Council officers were reported to view the information he imparted in Washington as minimal - ''chicken feed.''

President Reagan himself said the incident might have been ''a deliberate ploy, a maneuver,'' and added ''the information he provided was not anything new or sensational. It was pretty much information already known to the CIA.''

CIA officials have told the Senate Intelligence Committee they believe Yurchenko was a genuine defector who had second thoughts, in part because a lover in Canada broke off their affair, Senate sources have said.

The CIA document indicated that Yurchenko would have been in a position to provide a wide array of valuable information.

It said that from April to July of this year he had been deputy chief of the first department of the KGB's First Chief Directorate, in charge of gathering intelligence in the United States and Canada. The department supervised KGB agents here and in Canada and coordinated the KGB's work with other communist-bloc spy agencies here.

The CIA said Yurchenko himself personally supervised the KGB staffs in Ottawa and Montreal, Canada, supervised a section working against the United States on Soviet territory and selecting agents in the United States, the CIA said. He also supervised wartime plans for his department.

In 1959, Yurchenko transferred to the KGB from the Soviet Navy's submarine service, rising through its ranks with a foreign tour in Egypt in 1968-72, the CIA said.