In an unusual court appearance yesterday, a top CIA official gave jurors in the espionage trial of Larry Wu-Tai Chin a lesson on the basics of intelligence gathering.

John H. Stein, the Central Intelligence Agency's deputy director for operations, was one of four witnesses presented by federal prosecutors as experts on intelligence.

Chin, 63, is charged with espionage and conspiracy for allegedly having handed over classified information to Chinese intelligence officers since 1949 while working as an analyst and translator for the CIA's Foreign Broadcast Information Service (FBIS). He also is charged with violations of income tax and financial reporting laws.

Testimony from the intelligence experts was detailed but revealed little that is not widely known. Stein told the jury that "some 90 percent" of final intelligence reports, such as those seen by the president, come from overt or open sources. But personal contacts, which are mostly clandestine, are extremely important because "it is only through humans that you can get intentions."

Stein acknowledged later outside the courtroom that he could "not think of another example" in recent years of when a high-level CIA official testified at an espionage trial.

Chin's former boss, Cy Braegelmann, also testified, describing him as "one of the very best" Chinese translators in the Chinese section of FBIS' Rosslyn office. Braegelmann, who said he met Chin in 1970, testified that the Chinese section he headed handled an average of 50 classified documents a day.

He said, however, that only "once in a while" did guards conduct spot checks of people leaving the building because "everyone knew you could not take classified documents out of the building." Asked if employes were ever frisked or their clothing was checked, he replied, "Oh no, no."

An FBI agent testified Tuesday that Chin told him he put classified documents in his briefcase or coat pockets and took them out of the FBIS office to photograph at home.

Under cross-examination by Chin's lawyers, Jacob A. Stein and W. Gary Kohlman, John Stein and Braegelmann said they never saw any of the documents Chin is accused of giving to the Chinese.

The government has offered as evidence documents similar to those Chin had access to at his job.

Jacob Stein told U.S. District Court Judge Robert R. Merhige Jr. Tuesday that Chin will testify that the information Chin gave to the Chinese was not damaging and was to encourage a reconciliation between China and the United States.

Yesterday, his lawyers questioned the CIA's Stein about whether he knew in 1969 that President Nixon was secretly planning to normalize relations with China. Stein said he had not known. He also acknowledged that he had no direct knowledge of Chin's alleged espionage.

Federal prosecutors sought to stop defense attorneys from questioning FBI counterintelligence agent Mark R. Johnson about the FBI's original source on Chin's alleged spying, which the agency has declined to identify.

Johnson testified that during an interview last November that Chin speculated the source was a Chinese intelligence officer he had met in Hong Kong named Ou Qiming and that Ou had defected.

After a long bench conference, Merhige permitted defense attorney Kohlman to ask Johnson if he had "checked with Mr. Ou about the documents" Chin allegedly gave away. "No," was his reply.

Chin is expected to take the stand today.