The warfare in Vietnam and Cambodia has been accompanied in the last week by a series of government statements indicating that the third nation of Indochina, Laos, is being drawn into the Chinese-Vietnamese confrontation.

Laos has moved steadily closer to Hanoi since 1975 and an estimated 50,000 Vietnamese troops are in Laos helping the Communist government battle guerrilla opponents among the hill tribes and the Lao living on the southern plain.

"Relations between Laos and China have worsened with each passing day," Laos said two days ago.

A Lao government statement accused China of deploying "several divisions" of regular Chinese Army troops on the Chinese side of the mountainous Lao-Chinese border and carrying out "military exercises."

In addition, Laos said China has sent spies across the border to "create divisions among the Lao people of ethnic nationalities."

As they do along the Vietnam-China border, hill tribes live on both sides and they have a long tradition of relative independence of central control. Intelligence on what is happening at the border is hard to obtain here. But several Indochina-watchers said this week they are convinced China will stir up trouble as part of its effort to keep pressure on Hanoi and check Vietnam's growing control in Laos.

The sparsely populated border areas provide easy infiltration routes for the kind of spy activity Laos accuses China of sponsoring there.

The Soviet Union sounded the first alarm over Chinese intentions toward Laos when Chinese troops still were pressing their invasion of Vietnam. Mongolia and Vietnam quickly followed suit and then Laos issued its statement.

Laos signed a treaty of friendship and cooperation with Vietnam in July 1977, but it had seemed to be trying to maintain friendly relations with China even as Chinese-Vietnamese relations deteriorated.

Now, however, Laos has gone quite far in separating itself from China. It cited Chinese assistance to Laos during Laos' efforts to gain independence and said the Lao government tried its "utmost to preserve, safeguard and develop such a fine relationship."

The government statement said, however, that "by their acts, the Chinese rulers have destroyed the tradition of friendship and solidarity between the Lao and Chinese peoples."

Laos described its solidarity with Vietnam and Cambodia as "iron-like."

China has had troops in Laos building a highway from the border south to the former royal capital of Luang Prabang since 1962. When the United States was fighting in Indochina, Washington used to worry about the Chinese presence. Now the same roadbuilders worry the Vietnamese.

In addition to their prolonged construction work, the Chinese presumably have gained close knowledge of the northern Lao countryside.

A Chinese invasion of Laos similar to the action gainst Vietnam seems unlikely to Indochina-watchers here. Laos has a population of only 3 million. It is a far cry from the aggressive military power of Vietnam.

However, it seems likely that China could use disaffected hill tribes, like those that fought for the U.S. Central Intelligence Agency against the Communists when the United States was active in Laos, for raids and sabotage that would be a thorn in Vietnam's side.