The American military command systematically understated the true strength of Vietcong forces during the year before the Tet offensive on orders from Gen. William C. Westmoreland, the American commander in Vietnam, according to a CBS News documentary.

Westmoreland's intelligence officers knew false reports were being sent from Saigon to Washington, they acknowledge in the documentary.

The program, "The Uncounted Enemy: A Vietnam Deception," will be broadcast Saturday from 9:30 to 11 p.m. (WDVM-9).

According to the former intelligence officers, their reports were altered to conform with Westmoreland's contention that the Vietcong army in South Vietnam consisted of fewer than 300,000 men.

In fact, they say, on the eve of the Tet offensive in January and February, 1968, the Vietcong and North Vietnamese may have had twice that many troops in South Vietnam.

After Tet, which Westmoreland termed a great American victory but which the Joint Chiefs of Staff used as justification for requesting an additional 206,000 American troops, the American command in Vietnam (MACV) again altered intelligence estimates, according to CBS.

In the documentary, a MACV analyst named Richard MacArthur says he returned from a brief vacation after Tet to discover that his estimate of Vietcong guerrilla strength had been cut in half.

When he protested to a colonel in the MACV intelligence center, the officer told him, "Mac, lie a little, Mac. Lie a little," MacArthur said.

Two former intelligence officers say then-colonel Daniel Graham, an Army intelligence officer who later became director of the Defense Intelligence Agency, ordered that information in MACV's computers on Vietcong strength be altered after Tet.

This was necessary to avoid the impression that "we had almost no enemy left after Tet," according to one of the officers, because MACV was claiming such high Vietcong losses during the offensive without acknowledging the true level of enemy forces before the attack began.

In the documentary, Graham, now retired from the Army, but still an active spokesman for hard-line defense positions, denies he was responsible for altering information in the computers.

The fact that U.S. intelligence analysts differed sharply over estimates of Vietcong strength was previously known.

Sam Adams, a former CIA analyst who argued for higher estimates at the time, has since written and spoken about the argument, which previously appeared to be a dispute between civilians at CIA and the military.

Adams was a consultant to CBS producer George Crile for the documentary.

But this is the first time Army intelligence officers, including a general who was the senior intelligence officer in Vietnam, have said that numbers were deliberately faked. The general, Joseph McChristian, says in the documentary that in 1967 his estimates showed "that enemy strength was increasing."

McChristian concluded that the enemy could continue the war "for an indefinite period."

But Westmoreland rejected this finding and refused to report it to Washington. In the documentary, under intensive questioning from correspondent Mike Wallace, Westmoreland explained that his refusal was based partly on political considerations.

What was the political reason? Wallace asked.

Westmoreland replied: "Because, the people in Washington were not sophisticated enough to understand and evaluate this thing, and neither was the media."