Three years after their victory in the Indochinese war, Vietnam's Communist leaders have been hit by the same scourges that crippled their old American adversaries.

Hanoi is beset by an unwanted war against a small but intractable foe, economic dislocation, social disorder and even widespread draft-dodging.

Particularly in South Vietnam, where the U.S. backed government in Saigon surrendered to the Communists on April 30, 1975, young people have not looked "in a favorable light" on the task of "protecting the fatherland" against new attacks from Cambodia, Communists Party Central Committee member Pham Van Kiet complained in a speech that has reached here.

A continuing food shortage, worsened by reports of another bad crop, makes this year's victory anniversary celebration that much more sour.

Over and above its reluntance to manufacture rifles when it really needs plows, Hanoi has found the morale problems of war against a smaller power as real and frustrating as the Americans ever did. The Vietnamese army of 1978 appears to have little of the fervor - or success - of the victors of 1975.

The weary veterans and the disgruntled and hastily trained recruits from the conquered South were badly bloodied by the outmanned Cambodians in January. Vietnamese generals now seem hesitant to launch another major offensive.

Like war planners in Washington in the 1960s, the Vietnamese are also worrying about Chinese intervention. They have reacted to Chinese aid to the Cambodians and trubles on their own Chinese border by closing the small shops run by overseas Chinese in Ho Chi Minh City, formerly Saigon - leading to reported antigovernment demonstrations in which Ho Chi Minh City's Chinese have held up pictures of Mao Tse-tung.

But the Vietnamese leaders appear to realize that none of their new problems - most of them at least in part the result of the war that ended three years ago - can be solved until everyone has enough to eat.

Drought and cyclones cut deep into the last year's grain corp. Port inefficiency and corruption are slowing the movement of relief food. One visiting Yugoslav journalist reported that a chicken cost a Vietnamese worker half a month's pay. Mindful of all this, the government has cut back on industrial projects to devote all resources to agriculture.

Hanoi also appears to have made a concerted effort to soothe its Southeast Asian neighbors, who are understandably fearful of a nation with such a large, well-equipped army. Foreign Minister Nguyen Duy Trinh made a good impression in Indonesia, Malaysia, the Phillippines and Thailand during a turn-of-the-year journey of conciliation. Hanoi last year issued a set of foreing investment regulations designed to attract Western entrepreneurs.

Such a softening of Hanoi's previously hard-edged approach to the rest of the world appears to be neither unanimous or well-coordinated. Deputy Foreign Minister Vo Dong Giang marred an otherwise successful Manila trip by publicly lecturing the Filipinos on an issue very sensitive to them - their U.S. operated military bases. Business sources here said some European firms found the Vietnamese unwilling to honor their terms for reimbursement for nationalized plants, set out in the new investment regulations.

The Vietnamese have not shrunk from or disguised their worst problem, food shortages.

An exhaustive review of first quarter farming statistics broadcast by Hanoi last month revealed that the planting of rice and nearly every other crop was far behind schedule, despite the need to make up for last year's disasters. The broadcast said peasants were relying almost exclusively on animal manure while nitrogen fertilizer sat in the hopelessly snarled ports. Unusually cool weather has slowed growth of rice shoots; moths and other insects were thriving while water was short.

The radio said the nation faced "serious shortages" of fertilizer, peanuts, soybeans, sugarcane, hogs and beef. But unlike the Chinese, who have rejected all offers of charity in their recent economic troubles, the Vietnamese have gladly accepted the food and other aid from about 25 nations, including a 10,000-ton shipment of wheat from a U.S. church group.

Hanoi recently broke off dealings with a French firm, Creusot-Loire, which wanted to build a huge steel complex. Apparently farm development had to come first.

A Swedish paper mill project has also been delayed, apparently for the same reasons of inefficiency and a massive shift of priorities of farming.

"Import of a quantity of materials, spare parts and commodities in 1978 will be cut and that of a number of raw materials will be cut sharply," Vice Premier Le Thanh Nghi said.

Instead, Nghi said, investment for agriculture will be increased by 65 percent compared to last year.

It is unclear whether the Vietnamese can make much progress without more investment in the transportation industry that farming depends upon. Indian journalist Nayan Chanda, writing for the Far Eastern Economic Review about the latest of his several trips to Vietnam said he was "struck by the rundown state of the Chinese and Soviet trucks carrying heavy loads. Nearly 30 percent of Vietnam's vehicles are out of operation for lack of spare parts."

To jugde from the Vietnamese press, the social disorder and corruption accompanying the food shortage is at least as worrisome to the leadership. According to one broadcast monitored here, Communist Party General Secretary Le Duan told military academy graduates that "a number of negative aspects are still prevalent in the economic and social life in our country. All this has inevitably exerted a bad effect on our army units and on the sentiments, thoughts, actions and way of life of our cadres and combatants."

Northerners used to deprivation during the wars years have been stealing or extorting the relative riches of the conquered South. As Le Duan put it. "A lot of property belonging to the revolution in the newly liberated areas was under loose management."

In turn, Pham Van Kiet said, there is a "limited understanding displayed by the southern people in general, and the southern young people in particular, of the task of strengthening national defense for protecting and building the country."

The northern administrators have come down particularly hard in recent weeks on the nearly a million ethnic Chinese in the South, many of whom have been living off small shops in the Cholon district of Ho Chi Minh City. Such "bourgeois trading" will no longer be tolerated, the official press declared.

Peking, which has attempted to show concern for the Cholon Chinese despite their capitalist tendencies, has reportedly been rebuffed in attempts to send official representatives to the district.

This Peking-Hanoi war of nerves may also explain in part the warm tributes given exiled Chilean Communist, leader Luis Corvalan in Hanoi this past week, just as the official Chinese news agency was reporting political liberalization in Chile and Peking's new ambassador was presenting his credentials in Santigo.

The Vietnamese have denied reports of recent tank battles on the border with China but scuffles and occasional shouting matches continue, European diplomats said. Many tribal peoples in the mountains of northern Vietnam have relatives across the border in China. Peking has had some luck winning the allegiance of the tribes, and the emnity of Hanoi, by providing health services and cheap consumer goods on their side of the border.

The Vietnamese are daily promising better administrative regulations and more honest government personnel to improve their own services along the northern border and elsewhere.

One measure of Hanoi's failure so far to assuage such grievances in the this month compared to a 500-a month flow of illegal emigrants up to 3,000 average the first half of 1977. They are people who saw little to celebrate on liberation day 1975, and have found nothing in the Communists' mistakes and hard luck of the last three years to make them any happier.