The Kremlin, in a toughly worded commentary yesterday in the Communist Party newspaper Pravda, warned Peking to end its "unconcealed military pressure" on Moscow's ally Vietnam.

The Pravda article, whose signature "I. Alexandroy" indicated that it represents top-level Soviet views, said China was massing troops along Vietnam's northern frontier and provoking armed border incidents. Meanwhile, the Chinese Foreign Ministry, in a diplomatic protest, charged that Vietnamese troops had killed more than 70 Chinese border guards and civilians in clashes in the past three weeks.

The charges came one day after the United States issued a statement of concern about the possibility of expanded conflict in Southeast Asia. An invasion of Cambodia Dec. 25 by an estimated 100,000 Vietnamese troops in support of pro-Hanoi rebels succeeded in installing a new government in Phnom Penh.

According to reports from Thailand, Vietnam has sent part of a Vietnamese division stationed in Laos to reinforce its troops fighting guerrillas of the ousted regime in Cambodia.

Fighting there was reported to have diminished to a series of sporadic guerrilla attacks against the Vietnamese-led forces.

At the United Nations in New York, Cambodian Prince Norddom Sihanouk, who has been speaking in defense of the ousted Peking-backed regime of Premier Pol Pot, proposed the convening of an Indochina Peace Conference on the order of the one that produced the 1954 Geneva agreements on Southeast Asia.