Henry Kissinger (search) and other top Nixon administration officials worried about how they would explain to a skeptical American public their plan to expand the Vietnam War (search) to Cambodia and Laos, according to newly declassified documents.

A task force that answered to national security adviser Kissinger met several times before the United States and its South Vietnamese allies targeted North Vietnamese supply routes in Cambodia (search) in 1970 and Laos (search) a year later to discuss how to sell the policy to Congress and the American people.

The minutes of the Washington Special Actions Group are contained in some of the 180,000 pages of newly declassified Nixon administration National Security Council documents released Thursday by the National Archives. Another 140,000 pages remained classified despite the passage of more than 30 years.

Officials agreed at their meeting around the time of the April 1970 action that they would not publicly announce the invasion. Still, they anticipated inevitable questions, and decided to describe it as a continuing effort to end the communist sanctuaries.

"It's a support of the move against the sanctuaries and not an extension of it," said U. Alexis Johnson, undersecretary of state.

The strategy was less than successful: The invasion of Cambodia set off nationwide protests, including one at Kent State University in Ohio where National Guardsmen killed four students -- a watershed in turning public opinion against the war.

In February 1971, the United States gave the green light to South Vietnam's plan to go into Laos to cut off the North Vietnamese supply route. Kissinger wondered how to explain that action.

"The basic theme should be that this is a South Vietnamese operation aimed at preventing the rebuilding of the sanctuary areas," he said.

In 1972, Kissinger's then-deputy, Alexander Haig, delivered an upbeat assessment of the South Vietnamese army, then shouldering more of the fighting under the Nixon administration's policy of withdrawing U.S. troops.

Haig said South Vietnam troops, backed by U.S. bombing, had withstood a North Vietnamese offensive against several outposts.

"There is no sense of panic in Saigon," Haig declared. "Everyone was picked up by the strikes on the North."

Johnson, the State Department official, agreed. He said South Vietnam was overcoming its "inferiority complex. They always thought the North Vietnamese were 10 feet tall. Now they've seen they can beat the other side."

Saigon fell to the communists three years later.

The task force discussed other topics as well.

At a series of meetings in September 1973, after a military coup led by Gen. Augusto Pinochet ousted elected Marxist President Salvador Allende, U.S. officials worried about being seen as behind the regime change.

"We have to be careful to point out that we had nothing to do with the coup, which is true," said State Department official Kenneth Rush.

Privately, U.S. officials cheered the new military junta. "They are a conservative group, and I think we can talk turkey with them," said Adm. Thomas Moorer, chairman of the Joint Chiefs of Staff.

But the officials worried about being too supportive of the new leaders. The U.S. government quickly established informal communications with the Chilean rulers, but formal recognition of the new regime was still weeks away.

"The biggest errors we have made in Latin America in recent years have involved too hasty recognition of military regimes," State Department official Jack Kubisch said. "Publicly, we should avoid a too quick, affectionate embrace and any impression that we had any involvement in the coup."