Although Vietnam's war in Cambodia appears to be taking a growing toll on this country, a newly reshuffled Vietnamese leadership is showing no signs of fexibility toward international efforts for a settlement of the conflict.

With a U.N.-sponsored conference on Cambodia to open in New York Monday, Vietnam and its main allies -- the Soviet Union, Laos and the Hanoi-backed government in Cambodia -- are sticking to their refusal to attend. The conference, backed by the United States, China and Southeast Asia's noncommunist nations, is to present a plan for the withdrawal of Vietnam's 200,000 troops from Cambodia and elections to form a new independent government.

In Cambodia, meanwhile, the war appears to be at a stalemate, according to diplomatic sources in Bangkok. Western and Asian diplomats agree that the initiative now belongs to Hanoi's main foe in the war, the 30,000 to 40,000 communist Khmer Rouge troops led by ousted Cambodian dictator Pol Pot.

However, while Pol Pot's forces appear stronger now than at any time since the December 1978 Vietnamese invasion chased him from power, the Khmer Rouge still do not threaten fundamental Vietnamese control of Cambodia, the sources said.

At home the Vietnamese war effort appears to be having increasingly serious repercussion. There are hints of a small but spreading current of antiwar sentiment, especially among the young men of southern Vietnam who make up much of the occupation force in Cambodia.

Some proponents here of Vietnam's six-year-old communist government blame the war in large part for the country's severe economic difficulties. However, there is no public sign that this linkage is made by the senior leadership in Hanoi, and even the southern communists do not go so far as to advocate withdrawal of Vietnamese troops from Cambodia.

One of Vietnam's most serious economic troubles is a shortage of food, which has resulted in widespread undernourishment and low productivity.

"Malnutrition is getting worse because Vietnam has been at war for 30 years and continues to be at war," said Duong Quynh Hoa, a former health minister in South Vietnam's Provisional Revolutionary Government and now director of a pediatrics hospital in Ho Chi Minh City, which was called Saigon before the 1975 communist victory and unification of north and south.

"It is difficult for country at war to develop its economy," she said. "The economic problems here are very serious. We're in a war economy and it's not productive.

"I'm convinced that if Vietnam believed Cambodia would not be a threat, Vietnam would withdraw its troops and revive its economy," she said. "But we're obliged to be in Cambodia and it's a major handicap for us from the economic point of view."

While public opinion is difficult to gauge, foreign residents feel most Vietnamese are amvivalent, if not apathetic, about the war. It is rarely mentioned by the controlled news media or discussed in public. While Vietnamese mothers do not want to send their sons off to war, there has been little love lost between Cambodians and Vietnamese for centuries, and the war effort evokes a certain amount of patriotism even among noncommunist Vietnamese, one foreign resident said.

A 25-year-old worker here sees the problem differently, however. He is eligible for the draft and has been paying bribes of 200 to 300 dong ($50 to $75) periodically over the last couple of years to avoid military service.

"I don't want to go into the Army and fight in Cambodia," he said. He added that most of his friends had left the country, many to avoid military service, but that he could not affort the approximately $1,000 needed to finance an illegal emigration by boat.

According to a Hanoi-based diplomat, Vietnamese government leaders in the capital attribute the country's economic problems largely to mismanagement rather than to effects of the war effort in Cambodia. However, he said, there are some signs of concern about the cost of the war and about the prospect of growing dependence on the Soviet Union, Hanoi's main aid donor.

Nevertheless, a government reshuffle last week that installed 73-year-old Truong Chinh as president has not signaled any significant policy changes, least of all on Cambodia, diplomats said. "The Vietnamese government leaders have a very Soviet, almost Stalinist, state of mind," said one foreign resident. "Any negotiation or compromise on Cambodia would only be a pause. I see them as inflexible."

The Vietnamese position remains that any pull-out from Cambodia would invite the return to power of Pol Pot, who is held responsible for the deaths of more than a million Cambodians during his bloody four-year rule. This, the Vietnamese believe, would mean a hostile pro-Chinese presence on Vietnam's western border, which Hanoi regards as intolerable.

Western nations and Vietnam's noncommunist neighbors want a neutral government without Pol Pot, something Hanoi terms impossible.

Whether this current inflexibility may be modified by leadership changes in the future is a source of speculation among diplomats, who are looking to a Communist Party congress in December for clues to Hanoi's future course.

Meanwhile, the Khmer Rouge initiative in Cambodia has put Vietnamese troops largely on the defensive, according to Bangkok-based diplomats.

"Vietnam's capacity to wage war in Cambodia is being eroded," one Western Diplomat said. He cited intelligence reports of Vietnamese difficulties in getting units into position and keeping up supplies to troops as well as low morale and illness among those in the field.

"I'm convinced that the Vietnamese don't have what it takes militarily to knock out the Khmer Rouge," the diplomat said. He said the Vietnamese came close in 1979, but that the Pol Pot forces were able to recoup somewhat during the rainy season late in the year. "The last chance the Vietnamese had was in the dry season of early 1980," he said, but that offensive was hampered by logistical problems.

While the Khmer Rouge have done surprisingly well militarily in recent months, the diplomats said, they have failed to expand their political base and gain popular acceptance in a country that cannot forget their previous brutality. Moreover, the Pol Pot forces still do not control any major population centers and the vital rice-producing region in the center of the country remains in Vietnamese hands, the sources said.

The main strength of the Khmer Rouge now is its ability to attack the Vietnamese in hit-and-run raids. According to the diplomats, these have severely reduced Vietnamese use of strategic Route 6. In addition, the Khmer Rouge are said to have a fairly free run in northeastern Cambodia.Although sparsely populated, this area is considered important because it adjoins Vietnam's central highlands, where hill tribesmen have been waging a small insurgency against the Hanoi government.

The Khmer Rouge are also said to control much of the southwest in the region of the Cardamon and Elephant mountain ranges.

"Militarily it's a stalemate," said a Western diplomat in Bangkok. "I can't see the Vietnamese successfully crushing the resistance and I can't see the Khmer Rouge driving the Vietnamese out."

The noncommunist resistance led by expremier Son Sann has yet to become military factor, according to the diplomats, even though a new supply of Chinese weapons has allowed the group to nearly double its strength to perhaps 6,000 men.

However, the diplomats report that Son Sann has been more successful in political proselytizing, including in the Cambodian capital of Phnom Penh. He is said to have developed wide contacts among bureaucrats working for the Vietnamese-installed Cambodian government headed by Heng Samrin.