No one bothers anymore to repair the shattered windows and bombed-out roofs of this hapless town on the Sino-Vietnamese border.

Once a lively crossroads for the simple minority folk on both sides, Pingmeng is now caught in the cross fire of a five-year conflict between the two giants of Asian communism.

The human costs are reflected in the flight of a quarter of the town's inhabitants and in the sad faces of those who stayed behind to see their neighbors felled by snipers' bullets.

Yet, Pingmeng's very ability to survive on this fault line of Sino-Vietnamese relations underlines the limited nature of a dispute fought for advantages far from the border itself.

For all the the people's suffering, the fate of Pingmeng and other outposts along the 500-mile border is a diversionary sideshow in the larger struggle for influence in Indochina.

Border tensions heightened by the presence of an estimated 250,000 troops on each side have continued since 1978 not because of any real territorial dispute or ideological quarrel between Peking and Hanoi, but because the fight serves both countries' interests in Cambodia, where Peking-backed rebels are fighting the pro-Hanoi regime.

For China, the border issue is a handy pretext for opening a second front, diverting Hanoi's best troops from the Cambodian theater. As a political dividend, it allows Peking to show its armed solidarity with the rebels and with Southeast Asian governments fearful of Vietnam and its Soviet ally.

The costs are greater for Vietnam, which also has 180,000 troops in Cambodia. Still, it uses the border problem as a way to punish China and to cast it as a bully that threatens smaller nations.

As a corollary conflict, the border dispute generally reflects the intensity of fighting in Cambodia. Last spring, China and Vietnam exchanged artillery shots across their border after Hanoi opened a major campaign to mop up the pro-Peking insurgents along the Thai-Cambodian border.

At this time of rainy season hiatus in Indochina, however, the Sino-Vietnamese border appeared remarkably calm when foreign correspondents visited the Guangxi autonomous region last week.

Guangxi officials accused Hanoi of constant harassment, including 236 "armed provocations" in the first five months of this year. They charged the Vietnamese Army with shelling farmers, planting land mines in rice fields, stealing crops and sending over oxen with anti-China pamphlets tied around their necks.

"Our people have homes but they cannot go back to sleep; they have land but they cannot go back to till," said Deputy Foreign Affairs Director Zhang Guoliang.

Outside the briefing rooms, however, war seemed far distant from the gentle Guangxi tableau of water buffalo and sun-baked peasants planting rice seedlings on what is supposed to be China's tensest frontier.

Except for sentries at border points and a few Army vehicles, there was no visible military presence just three months after reports of artillery battles in the region.

The occasional antiaircraft guns and Army camps I spotted in the same area 2 1/2 years ago were gone.

At Friendship Pass, the ironically named border crossing through which China sent its troops to invade Vietnam in 1979, military officers were preparing not for battle, but for the return of enemy prisoners later this month.

Though guarded by soldiers perched on jagged mountain cliffs, the pass seemed as peaceful as a tourist site. Earlier in the day, a hand grenade exploded near a border checkpoint. But it reportedly had been detonated by fishermen trying to increase their catch.

The place looked exactly as it had on the last visit except that four large photographs had been removed from a tower overlooking the barbed-wire boundary separating the socialist states. The pictures had been of Marx, Lenin, Stalin and Mao.

With the guns of Cambodia silent for now, even Pingmeng appeared to be enjoying a normal life, albeit under the supervision of 500 soldiers scattered throughout the country town and its surrounding fields.

Less than 500 yards from the border, children played in a dirt road flanked by armed guards. Old women stooped in front of their flimsy wooden houses, washing clothes or sewing.

Although the town had drawn some enemy fire in April, the official reports of damage were greatly exaggerated, apparently to justify Chinese retaliation, or at least propaganda claims of retaliation.

China was then trying to appease Thailand, which had said its frontier was being violated by Vietnamese troops chasing Cambodian rebels across the Thai-Cambodian border. Peking had long promised to aid Bangkok if Vietnam's raids spilled onto Thai soil.

On April 19, the official New China News Agency accused the Vietnamese Army of "blowing up" the primary school, hospital and 11 other civilian buildings in Pingmeng.

The report said Chinese artillery returned the fire, causing "heavy losses" to Vietnamese troops.

Diplomats in Hanoi, less than 100 miles from the front, said Chinese claims of strong retaliatory attacks were invented, probably to gain propaganda points with Bangkok.

Foreign correspondents discovered the official accounts of Pingmeng's damage to be fraudulent as well.

Buildings said to have been blown up were very much intact. Some suffered superficial damage--a hole in the roof here, broken glass there. None of the structures had been occupied during the shelling.

The school never was hit, although nearby blasts knocked out a few windows hours after the children left for home.

The hospital, which had been evacuated 13 months earlier, was struck by a howitzer shell that penetrated a fourth-floor wall, dropped through the floor and went out the third-floor window without exploding.

Residents brought out a thermos bottle and kitchen pan, each bearing a single bullet hole, as proof of enemy fire, but no human casualties were reported.

"We always have enough time to get into underground shelters," said Liang Youqian, 28. "You get used to it."

Regardless of official hyperbole, living on the firing line requires more than a little adjustment. Shelling is relatively rare, but uncertainty about indiscriminate violence is almost as bad.

A 57-year-old woman returning from the fields in April of last year was shot in the left thigh and still cannot walk well.

A 16-year-old boy was killed by a sniper's bullet while standing in front of his house a month earlier.

"Nobody knows when the shells will come," said Pingmeng militia chief Li Chaowei, 30. "Sometimes our people dare not to go out of their houses."

An innkeeper surveying the roof damage caused by artillery shells last year said he has not made repairs for fear of another attack.

The irony of Pingmeng is that it once was a center for Sino-Vietnamese friendship, a meeting place for sporting events and peasant trade. The hospital evacuated because of the current hostilities had opened its doors to Vietnamese until a few years ago.

On the basketball court where teams from both sides once played together, the goal posts are inscribed in Chinese characters: "Friendship first, competition second."

The late Vietnamese president Ho Chi Minh found refuge in Pingmeng while fighting French colonialists in the 1940s and then fed his troops locally grown rice during the U.S. war with Vietnam two decades later.

The most telling symbol of the flip-flop in relations is a white three-story building that Pingmeng officials had begun constructing in the late 1970s as a reception center for Vietnamese guests.

The nearly completed building about 100 yards from the border is riddled with bullet holes; its plaster walls are caving in. Sentries holding automatic rifles peer from the second-floor balcony.

"The people of Pingmeng are witnesses to the transformation of relations between China and Vietnam," said Pingmeng commune leader Wei Youxing.