The strains of staying mobilized in fear of another Chinese attack and of supporting its forces in Cambodia have reduced Vietnam's economy to a shambles, according to intelligence reports and eyewitness accounts.

The economic situation, sources said, is forcing Hanoi's leader to turn to the Soviet Union for emergency help in the form of food, industrial equiptment and weapons to replace those lost in battles inside Vietnam and in Cambodia.

Although intelligence officers believe Vietnamese leaders are resisting Soviet requests for permanent bases in Vietnam, the Russian presence there has increased, now including about 4,000 technicians.

The Moscow-Hanoi connection, forged in formal terms by a "peace and friendship" treaty last November 3 and tightened in reaction to the Chinese invasion, is reported to include these elements:

Soviet procurement of rice and assurances of other grain supplies to make up for serious food shortages in Vietnam. U.S. officials predict that, despite Moscow's own shortages, the Soviets will supply nearly all of the 2 million metric tons of grain that Vietnam needs to feed its people, its military forces and the dependent pouplation in neighboring Cambodia.

Soviet shipments of about 70,000 metric tons of military and industrial equiptment into Vietnam so far this year, more than twice the tonnage Russia supplied last year. Items include industial generators, MIG19 and MIG21 aircraft and 1,000 trucks -- possibly to speed the distribution of rice through Vietnam and to troops in Combodia.

Construction near Cam Rahn Bay of a dish antenna radio monitoring station to manned by several hundred Soviet technicians, evidently to monitor chinese communications.

The periodic use of Vietnamese ports by Soviet ships and aircraft. U.S. officials said it does not appear that Vietnam has granted base rights to the Russians. However, recent port visits of a Soviet destroyer to Da Nang and a Soviet diesel submarine and submarine tender to Cam Ranh Bay effectively extend to range of Russian military power in Asia. The same can be said of Dan Nang stopovers in April and May by Soviet TU95 long-range reconnaissance aircraft, one flight of two planes in each stopover.

Vietnamese officials have described close ties with the Soviet Union as being necessary for self-preservation in view of the continuing conflict with China. In this perspective, one of the results of China's 17-day invasion early of year was to strengthen the Soviet-Vietnamese collaboration that the military action was intended to oppose.

Before and during the short-lived invasion of a mountainous border area, China amassed a force of close to 500,000 troops and more than 1,000 warplanes in the immediate area. Most of those troops and virtually all of the best aircraft have been withdrawn to their original stations elsewhere in China, according to U.S. officials.

The chinese redeployment does not seem to have eased vietnam's concern, however. An American church official, Murray Hiebert of the Mennonite Central Committee, said he was told during a recent trip to Hanoi that another Chinese invasion is expected after the rainy season this fall.

"Everywhere you go in the north are military preparations, people spending two hours a day in training, marching, firing guns," Hiebert said. He said bomb shelters covered over after the war against the United States are being redug, that old people are beng evacuated from Hanoi and that "shadow ministries" have been set up in Ho Chi Minh City, formerly Saigon, in case Hanoi is put out of commission.

Hiebert and other visitors reported trenches and other defensive earthworks being dug between Hanoi and the Chinese border. One visitor said new caves, evidently for artillery, have been dug in the hills near the border.

U.S. analysts in Washington estimate that about 200,000 Vietnamese troops now are positioned between Hanoi and the Chinese border, compared to 50,000 to 70,000 troops before the Chinese attack.

Policy-level American officials agree that there is little or no likelihood of a resumption of fighting between China and Vietnam in the next several months and probably for the rest of this year. But they also agree that if fighting should be resumed, it is likely to be on a much larger scale than before, because of the augmentation of Vietnamese forces along the Chinee border.

There is no clear consensus on the chances for a resumption of the battle. One senior official has cited the likelihood for a new Sino-Vietnamese war next year as "50-50," a high probality as such estimates go. However, the basis of these odd is said to be instinct, rather than concrete information. Some other officials believe the chances for new fighting are much more modest.

Vietnamese troops continue to be heavily engaged in fighting and in occupation duty in neighboring Cambodia. Chinese-based guerrillas led by Pol Pot continue to threaten the Vietnamese there, although most of the guerrillas apparently have been force into remote enclaves.

U.S. intelligence now estimates that as many as 23 Vietnamese divisions are in Cambodia, including elements of nine divisions along the Cambodian-Thai border. Some of these are new units created in the past several months.

To make up for combat losses and to meet the requirement for more forces in Cambodia and along the Chinese border, Vietnam is now dipping into its 17-year-old citizens for troops, U.S. analysts reported.