The Soviet reaction to China's attack on Vietnam continues to be marked by intense propaganda outbursts, but no inclination toward direct involvement on behalf of the Kremlin's important Southeast Asian ally is detectable here.

The Soviets are reported to have stepped up shipments of military supplies to Hanoi, beefed up their intelligence fleet off Vietnamese waters and increased aerial surveillance near China's borders. None of these are seen as more than cautious and expectable military moves to observe the fighting and bolster Vietnamese materiel.

It is unconfirmed whether the Soviet Army has been placed on a higher alert status, and there have been no reported alterations of Soviet troop dispositions along the heavily reinforced 5,000-mile border with China.

At the same time, seasoned observers here caution that the Soviets have an enormous stake in their Southeast Asian allies, glorying in the recent Hanoi-Moscow friendship treaty.

"I assume the Soviets don't want a military clash," declared one source, "but if something does not happen to reassure them that the Chinese are coming out in the next four or five days, they may feel compelled to act. You can't tell how long they will wait." This observer's opinion is that "it is a matter of days rather than weeks" for a Soviet decision.

At the same time, while noting that "the Soviets have the capabilities on the border to really deal a punishing blow to the Chinese," a source long exposed to the Soviet frame of mind said, "but they are not psychologically ready to do it."

Internal propaganda, considered a gauge of preparation of public opinion for government initiatives, has not reflected any impulse toward intervention. Themes of "solidarity and support" for the Vietnamese, struck early last week, continue to be a staple. Workers call for a relief fund, and public sentiment so far is clearly in favor of sending arms, not men.

Defense Minister Dmitri Ustinov, in a speech marking both Soviet Armed Forces Day and his own "candidacy" for election to the Supreme Soviet, said Friday that the "perfidious" Chinese attack "revealed before the whole world the real nature of its hegemonistic policy."

"The Soviet people wrathfully condemn the adventurist actions of the Peking leaders and resolutely demand an end to impudence by the Chinese aggressors," he said. "They unanimously declare their full solidarity and support for the Vietnamese."

As other leadership figures have done all week, Ustinov invoked the official Kremlin statement of Feb. 18, which warned Peking to withdraw immediately "before it is too late" and committed the Soviets to comply with the defense consultation clause of the friendship treaty signed here last November.

The defense article of that treaty, which is not a military alliance, requires immediate mutual consultations" in event of attack" for the purtions" in event of attack "for the puring appropriate effective measures to ensure the peace and security" of the signatories.

Soviet Foreign Minister Andrei Gromyko has met once with Vietnamese Ambassador Nguyen Huu Khieu, and no other meetings have been reported in the official press. Penetrating the opaque surface of the government has been especially difficult; official Soviets who usually are available to talk informally with Western journalists have not been available this week.

Western interest here is focused in part on the question of Soviet war supplies to Hanoi. A limited Soviet airlift reportedly has begun and it is believed the Vietnamese have asked for -- and will receive -- additional antiair-craft missiles to bolster Haiphong harbor defenses. The Chinese air force, although outmoded, outnumbers Hanoi's about 10 to 1.

It has been reported that the Vietnamese turned down a Soviet request for base facilities at Camranh Bay, the U.S.-built port in the southern part of the country. It is possible that the Soviets now may push anew for access there, pleading logistics problems. A Soviet presence there would be a valuable strategic point for Moscow, causing problems for the United States.

Serious Moscow-Hanoi differences were hinted at during the treaty talks, but it is not known what they were. The Soviets, seeking perhaps to put the best face on matters in the past week, have repeatedly emphasized Vietnamese "resoluteness" and ability to fight their own battles.

Soviet propaganda has said the fact that the invasion came two weeks after Chinese Vice Premier Teng Hsiaoping completed an official visit to the United States is no coincidence. The two nations are to exchange ambassadors Thursday as part of the normalization of relations. The Soviets have accused the United States in increasingly harsh terms of connivance in the attack, and have rebuked President Carter for not publicly condemning the Chinese. Carter has called on Peking to withdraw and asked Moscow and Hanoi to exercise restraint.

The Soviets seem to be in the grip of paranoia over the Chinese and mesmerized by the notion of "encirclement" by a powerful new alliance of their "hegemonistic" Peking adversaries with the United States and Western countries. Despite Soviet initiatives in Africa with Cuban troops, the Kremlin sees itself essentially as embattled.

If nothing else, the Peking visit of Treasury Secretary W. Michael Blumenthal despite the invasion serves to reinforce the Soviet view that the United States is determined to intensify its relations with Peking regardless of possible cost to U.S.-Soviet relations. It is not lost on the Soviets that the White House last summer postponed a similar trip here by Blumenthal to protest the political trials of dissidents, which the Soviets interpreted as unwarranted U.S. pressure in a purely internal matter.

The Communist Party newspaper Pravda today criticized Blumenthal for visiting China at a time it was "waging an aggressive war" in Vietnam.

The Chinese invasion means yet more strains on the Moscow-Washington relationship, although both countries continue to move toward final agreement on a new strategic arms limitation treat (SALT), which is the cornerstone of the superpowers' relationship.