Walt W. Rostow, one of President Lyndon B. Johnson's closest advisers at the height of the Vietnam war, today denied an assertion by CBS that General William C. Westmoreland gave the president "mostly good news" about Vietnam, leaving him unprepared for the communists' massive Tet offensive in 1968.

Testifying on behalf of Westmoreland in his $120 million libel suit against CBS Inc., Rostow said his memory of the substance and tone of a crucial April 1967 session at the White House was different from the version CBS broadcast in its 1982 documentary "The Uncounted Enemy: A Vietnam Deception."

In the documentary charging a conspiracy by top military leaders to suppress information about enemy strength from the president and the public, CBS interviewer Mike Wallace said Westmoreland assured Johnson that day that the Viet Cong's army had leveled off at 285,000 men and that the United States was "winning the war of attrition."

But on the stand Rostow, Johnson's special assistant and a member of the National Security Council, said it was "not my recollection" that Westmoreland made such a claim. Instead, he said Westmoreland -- commander of ground troops in Vietnam from 1964 to 1968 -- told the president that he needed 200,000 more soldiers to end the war in two years. Otherwise, Rostow said, the general predicted a five-year war in Southeast Asia.

According to transcripts made available by CBS during the lunch break today, Westmoreland said in an unbroadcast segment of the Wallace interview that he was "ordered" back from the front to brief the president and that he told Johnson that enemy troop strength had leveled off at 285,000.

Rostow, 68, now a professor of political economy at the University of Texas, told reporters outside the courtroom that although he was appearing to support Westmoreland in the CBS case, "I've got no ax to grind."

"It's right that I'm here and wrong that I wouldn't be," he said.

Author of 24 books, Rostow weathered the 4 1/2 hours of questions with a confidence and occasional ebullience that characterized his dealings with the press and public almost 15 years ago, when he was considered one of the administration's most optimistic officials about the course of the war.

He exhibited only one moment of irritation when CBS attorney David Boies began to ask him to recall specific estimates for the number of North Vietnamese infiltrating South Vietnam in the winter of 1967 before the Tet uprising in January 1968.

Pressed on what his "best advice" to Johnson would have been if the president had asked for an estimate in December 1967, Rostow said in a clipped voice: "I would have told him I could not in good conscience have given him a number.

"And I would add that he was too wise a man to have put a question like that about a war like this one," he added.

Rostow said in his testimony that some intelligence reports, including information on the stream of North Vietnamese infiltrating the south, took longer to get to the president than information from the National Security Agency, which got up-to-the minute reports on troop movement along the trails.

Rostow said sensors along the roads could pick up sounds and transmit them to U.S. listening posts. "But they were not perfect," he said. "Sometimes what they picked up were elephants or animals. So they were not perfect, but they were helpful."

At issue in this long trial is whether Westmoreland suppressed larger enemy troop estimates from the president because the numbers could have created a political bombshell at a time when Johnson, Rostow and Westmoreland, among others, were saying that the U.S. military was winning the war in Vietnam.

Westmoreland has charged that the CBS documentary converted a debate about the figures between the CIA and the Army into a conspiracy.

Rostow denied any pressures by Johnson or others for the general to keep the numbers down to maintain public support for predictions that the war was going well.

Speaking in the present tense about Johnson, who died in 1973, Rostow said he was "confident" that the president wanted no political slant in official intelligence data.

"I know him well enough to know that he would be angry and furious if he thought that a political estimate had been used in the making up of the estimate itself," Rostow testified.

Rostow, who was Westmoreland's first supporting witness, wrote a memo after the CBS program aired that called it a "serious misrepresentation." The memo, which is not a part of the trial evidence, said that even if Westmoreland had ordered a "ceiling" on estimates of enemy troop strength, "it in no way prevented the White House from forming a strikingly correct assessment as of late November and early December 1967 of the maximum effort the communists were about to undertake."