In testimony crucial to CBS in its defense against retired general William C. Westmoreland's libel suit, retired major general Joseph A. McChristian said today that Westmoreland had refused to send an important cable to his superiors in May 1967 for fear that it would "create a political bombshell" in Washington.

McChristian's description of the meeting at which he showed Westmoreland higher enemy troop figures for the first time contradicted Westmoreland's testimony more than three months ago.

As McChristian testified against his commander in Vietnam and fellow West Point graduate, Westmoreland sat frowning and red-faced at the plaintiff's table, occasionally shaking his head at McChristian's version of the meeting.

"I took that cable in to Gen. Westmoreland, and I stood in front of his desk and I handed it to him," said McChristian, who was in charge of military intelligence for Westmoreland at the time.

"I gave him a little bit of the background on what it was. He read it. He looked up at me and he said, 'If I send that cable to Washington, it will create a political bombshell.' "

CBS lawyer David Boies asked, "Sir, are you absolutely positive Gen. Westmoreland used the term 'political bombshell' during that meeting?"

"Yes, I am." McChristian replied firmly. "I am just as sure of it as I am seeing people in front of me right now. I was so surprised by it that there were enough words said there that burned themselves right into my memory . . . ."

On Nov. 16, when Westmoreland was asked by his lawyer, Dan M. Burt, whether he said "in words or substance" that the cable would cause "a political bombshell," the general testified, "I am confident I did not use those words."

He later added, "My recollection is I said something to this effect, 'Joe, if this cable goes in without further explanation, it will create a public relations problem.' "

At issue in Westmoreland's $120 million libel action is a 1982 CBS Reports documentary that accused him of participating in an alleged "conspiracy" to impose a ceiling on the reported number of enemy troops in order to maintain support for the war.

Westmoreland testified that he had overruled McChristian when McChristian wanted to send a cable showing higher figures for the enemy's "home militia," telling him, as Westmoreland recalled it, "We are not fighting those people. They are basically civilians."

Reading Westmoreland's testimony to the court, Boies asked McChristian:

"Did Gen. Westmoreland say that to you at that meeting in words or substance?"

"No, sir," McChristian replied. He added that if Westmoreland had made that comment, he would have reminded him about a conference three months earlier when top intelligence officials had decided to include those troops in the official enemy count.

In a memo McChristian apparently had written to himself, the 70-year-old Floridian said that Westmoreland phoned him two days before the CBS show aired in January 1982 and was "very upset" about what McChristian appeared to have told CBS.

"He said that he thought our converstion in May 1967 was private and official between West Pointers," McChristian wrote in the memo, which was subpoenaed by Westmoreland's lawyers.

"I replied that I spoke the truth. He said that he did not question my integrity, but maybe my judgment, that I had been used by CBS. He said that he has stood up for and took the brunt of Vietnam for all of us. He as much as accused me of being the one mainly responsible for his integrity being impugned."

McChristian had complained to CBS producer and codefendant George Crile after the show that the tape of his answer to a hypothetical question was edited to sound like a criticism of Westmoreland.

He also carefully avoided criticizing Westmoreland directly on the witness stand, even though he challenged Westmoreland's version of their key meeting.

When Boies asked him if he believed it was "improper for Gen. Westmoreland to hold your cable?" McChristian replied:

"I think that for a military man to withhold a report based upon political implications would be improper."

Under cross-examination by Westmoreland attorney David M. Dorsen, McChristian acknowledged that shortly before he was transferred from Vietnam in June 1967, he learned that U.S. Ambassador Robert Komer had ordered a reorganization of the intelligence operation that would have destroyed much of the intelligence system that McChristian had caused to be put in place.

He said that when he stormed into Komer's office and began to complain, the ambassador, who previously had headed President Lyndon B. Johnson's so-called pacification program, simply "looked up and said, 'Have a good trip home, Mac.' "

After Westmoreland listened to the same complaints and said "don't worry about it," McChristian, who was leaving the country that day, said he "felt like I had been kicked in the stomach."

However, McChristian denied that he felt any animosity toward Komer or the man who replaced him as intelligence chief, Brig. Gen. Phillip Davidson, both of whom testified for Westmoreland.