In an unusual accolade for the performance of U.S. intelligence agencies, a House subcommittee chairman reported yesterday that they "served the nation well" during the recent Chinese invasion of Vietnam.

Rep. Les Aspin (D-Wis.), chairman of the House Intelligence subcommittee on oversight, said in a written report that the Central Intelligence Agency provided at least six weeks' warning that China might take the action it did.

He said his findings were based on classified testimony before the subcommittee by State and Defense department officials.

Aspin quoted an "alert memorandum" issued by the CIA in early January as concluding that "the Chinese may choose to engineer a strong localized demonstration of Chinese power along the [Vietnamese]frontier."He said the CIA continued to reinforce this view until the Chinese attack into Vietnam's border area on Feb. 17.

On the other hand, he reported that U.S. agencies "had trouble in assessing the likelihood of Soviet involvement"as China moved to the attack.

He quoted a report by the Strategic Warning Staff, jointly manned by the CIA and the Pentagon, as saying the Soviets "almost certainly will attempt... counterpressures along the Sino-Soviet border.

This view was revised later to recognize that the likelihood of Soviet intervention would depend on the depth of China's penetration into Vietnam, Aspin said.

As far as is known, the Soviet Union made no move against China along their common border. China had anticipated Soviet actions by evacuating large numbers of civilians and some vulnerable military units from the area near the Sino-Soviet border.

Aspin said a memorandum published by U.S. intelligence agencies last November erroneously held that Vietnam would not overrun all of Cambodia -- as Hanoi forces actually did, starting around Christmas.

However, he said the Strategic Warning Staff argued it is "difficult to believe" that such a large Vietnamese force deployed along the Cambodian border was intended for only a limited objective.

Aspin said, from a policymaker's viewpoint, intelligence shortcomings in this situation were "minor" compared to the overall success in following Vietnamese military preparations.

On the whole, he concluded, the ability of U.S. intelligence "rapidly to observe, assess and report military preparations informed policymakers of impending Vietnamese, Chinese and Soviet actions well in advance."

He also praised the recent practice of permitting the full presentation of competing views, which he attributed to CIA Director Stansfield Turner.

Aspin suggested that the airing of competing views should be continued and strengthened, based on the record of intelligence performance in the Sino-Vietnamese war.