Former Central Intelligence Agency analyst Samuel A. Adams, whose theory on Vietnam is central to a CBS documentary now the subject of a trial here in federal court, said today he decided 17 years ago that "there had been a deception" on enemy troop estimates in Vietnam.

Adams, a codefendant in retired general William C. Westmoreland's $120 million libel action against CBS, told the jury that he resigned on Jan. 31, 1968, from a CIA branch in charge of estimating the Viet Cong and charged that his agency had "caved in" to Westmoreland's command on enemy troop data.

In the letter announcing his decision, Adams called the purported CIA compromise with the military, an agreement that he believed vastly underrated the number of enemy troops in Vietnam at the time, a "monument of deceit."

Adams, the first "live" witness for CBS after dramatizations and films of witnesses interviewed before the trial, testified after CBS lawyer David Boies showed the courtroom excerpts of an interview Adams did about three years ago with codefendant Mike Wallace.

In the excerpts shown on television monitors, Adams said his resignation came after he had estimated more Viet Cong in Vietnam than the agreed total in the official Order of Battle.

He said he believed that his predictions were confirmed during the Tet offensive beginning Jan. 30, 1968. Tet, an orchestrated attack by the communists on all major cities in South Vietnam and on the U.S. Embassy, was a "political victory" for the Viet Cong, Adams said.

"We had dug our own grave. We had been telling everybody right and left, in the papers, everybody, that this thing was being won, that the enemy's manpower was declining, when it was all baloney," he said on the film, which was not part of the broadcast at issue in this case.

"After that Tet , nobody believed anything that Westmoreland said. Nobody believed anything that the United States government said, and for good reason: because we'd been lying for months before Tet about the strength of the enemy," he said.

"And about their inability to mount anything like the Tet offensive," Wallace said on the film.

"And about their inability to mount anything like the Tet offensive," Adams repeated.

Adams, who was paid $25,000 as a consultant to the "CBS Reports" documentary unit, spent most of the last decade researching his thesis that the military suppressed higher enemy figures in 1967, apparently to maintain public support for the war.

The thesis was central to the Jan. 23, 1982, CBS documentary -- "The Uncounted Enemy: A Vietnam Deception." That documentary charged Westmoreland with being part of a "conspiracy" to keep greater enemy troop numbers from the public, Congress and the president.

Westmoreland, charging that the broadcast was untrue and that he was "rattlesnaked" by Wallace and his team in his interview, says he was defamed when the program accused him of hiding intelligence from his superiors, including the president. Such action by a military officer would be a breach of duty, his lawyers have said.

In a mini-summation of the case today, one of Westmoreland's lawyers, David Dorsen, told the jury that as they listen to CBS' witnesses over the next few weeks, they should ask themselves "whether one of those people has ever said that he met Gen. Westmoreland in his life."

Westmoreland's witnesses over the last three months have tried to portray Adams as a man "obsessed" with his theory. His former boss at the CIA, George Carver, told the court that Adams "tended to regard all those who disagreed with him as either fools or knaves."

Adams told the court that a cable attributed to him and used by Carver to show that he had "gone off half-cocked" was written by another CIA analyst, Dean Moor. However, Adams said he did sign off on the cable that called Westmoreland's command estimates of the enemy "totally unworkable." Westmoreland's witnesses have described the differences on enemy estimates as an "honest debate" instead of a conspiracy.