Investigators believe that retired CIA analyst Larry Wu-Tai Chin was given intelligence training by the Communist Chinese in the early 1940s, before he started working for the U.S. government, and was planted as a spy at the start of his more than 40 years of U.S. government service, according to officials familiar with the case.

The officials said Chin, who started working for the U.S. Army Liaison Office in China in 1943 and joined the CIA in 1952, had access to nearly all U.S. intelligence analysis concerning Asia while at the CIA.

As a "document control officer," Chin, 63, was responsible for routing "finished" intelligence reports through the CIA and to officials in the White House and other departments, the sources said.

Chin, who held high-level "code-word" clearance, is believed to have given the Chinese much of the information to which he had access, including reports during the war in Vietnam, they said. Chin is believed to have received more than $1 million from the Chinese in return for the information, one source said.

"It's astounding," said one government official familiar with the investigation. "He survived all the security checks and survived all the re-examinations."

Chin, who worked primarily as an analyst and translator for the CIA's Foreign Broadcast Information Service, "was more than a guy . . . listening to People's Republic of China broadcasts and translating the People's Daily," said one source familiar with the investigation.

U.S. intelligence officials are still assessing the damage that Chin might have caused but believe it represented a serious security breach, sources familiar with the investigation said.

"He wasn't a Walker and he couldn't do that kind of damage," one official said, referring to Soviet spy John Anthony Walker Jr., who pleaded guilty in October to masterminding an espionage ring that operated since 1968.

However, the source said, Chin provided "enough information to cause the Chinese to decorate this man." According to an FBI affidavit, Chinese intelligence officials decorated Chin with the title of "deputy bureau chief" for his work.

Some current and former intelligence officials played down Chin's role and said they were not aware he had access to extremely sensitive documents.

An FBI agent testified at a hearing for Chin last week that his deliveries to the Chinese were so voluminous that it took two translators two months to translate each shipment. The agent, Mark R. Johnson, also testified that Chin was feted as the guest of honor at a 1982 banquet in Peking attended by the head of China's intelligence service and its retired chief.

Johnson said Chin had clearance to see information "top secret and above."

Sources said Chin received the CIA's career intelligence medal for superior service when he retired in 1981. Chin, who continued to work for the CIA as a consultant until his arrest Nov. 22, was asked five months ago to return to the agency full time, his lawyer said at a court hearing last week.

A source familiar with the investigation said that was an apparent blunder on the part of CIA officials who asked Chin to resume full-time work rather than a ruse to aid the FBI's investigation, which began in December 1983. It has not been disclosed what triggered the probe.

Much of the government's case against Chin comes from Chin himself, who admitted spying for the Chinese in an interview with FBI agents before his arrest, according to an FBI affidavit and court testimony.

Investigators believe Chin, who was born in Peking and became a naturalized U.S. citizen, was given intelligence training while he was a college student in China during the early 1940s, the sources said.

During that period the Communists were engaged in a bitter struggle with the Nationalist Chinese Kuomintang for control of the government. The Communist Chinese government was formed in 1949.

While the FBI has suggested in an affidavit that Chin was recruited as a spy before he joined the CIA in 1952, it has not been disclosed before that Chin was allegedly groomed to become an intelligence agent a decade before that.

The affidavit states that Chin, while serving with the Army Liaison Office from 1943-44, met a "Dr. Wang" who "indoctrinated Chin on the aims of the Chinese Communist Party." In 1948, while Chin was working as an interpreter at the American Consulate in Shanghai, Dr. Wang introduced him to a "Mr. Wang of the Shanghai Police" who "encouraged Chin to serve the interests of Communist China."

The first indication that Chin actively engaged in espionage was in 1952, when, according to the affidavit, he was paid $2,000 by the Chinese for information about the location of Chinese prisoners of war in Korea and the type of intelligence information that American and Korean intelligence services were seeking from the POWs.