There is no love lost in this narrow, winding valley connecting China and Vietnam.

Rather, danger and uncertainty grip the peasants who fled from here to the safety of nearby caves, the refugees who passed through in search of asylum and the soldiers perched on mountain cliffs high above the border waiting for another war.

The front door to South China still is officially called Friendship Gate, an imposing, wedding-cake structure set down on a spacious plateau by Ming Dynasty warriors 612 years ago.

The Chinese soldiers who now guard this hostile mountains corridor 90 miles from Hanoi have renamed its entrance "the friendship gate without friendship."

The gray, fieldstone gateway opens to a part of China that has not been visited by American journalists for many years -- a rugged, hilly frontier that has channeled southbound Chinese armies for 2,000 years, the 1979 Vietnam invasion being just the most recent.

On the top floor of the gate building, photographs of the communist pantheon from Marx to Mao cover the walls of an empty room, looking out at a scrub-bush slope descending to the border where crossed logs and barbed wire separate the communist powers of Asia.

When China and Vietnam were socialist allies a decade ago, the rail line coursing through the pass carried millions of tons of Chinese war material sent south to aid Hanoi's conquest of South Vietnam. The tree-lined courtyard just inside the gate hosted friendly gatherings of Chinese and Vietnamese officials. Poor rice farmers on both sides of the border cultivated the hilly pockets of the valley with little regard for national boundaries.

Today the rail lines are overgrown with thick underbrush, the rolling terrain uninhabited and pocked by bomb craters, reflecting some of the fiercest fighting of the Sino-Vietnamese war two years ago.

Edgy border guards posted on the ledges of craggy, limestone hills exchange the latest barracks rumors about Vietnamese plans for a new attack. From the peak of Golden Chicken Mountain, the soldiers focus their binoculars on the high bamboo groves south of the border where Vietnamese artillery still lob shells into the valley and nearby villages.

Unlike the frozen isolation of Manzhouli Pass on the northeastern Sino-Soviet border, the Chinese Army aggressively defends this critical southern invasion route -- one of the few passable entry points along the 500-mile border China shares with Vietnam.

Set back a few miles from Friendship Pass, the front line of what is believed to be an army of 250,000 camps in the dense, tropical forest. China is said to have as many troops in its two southern provinces today as when they marched down the pass in February 1979 to teach some "necessary lessons" to Vietnam for expelling its ethnic Chinese residents and stirring border trouble.

Two years after the war, the border bombardments by Vietnam are reported to be greater in number and intensity than during the months before the 1979 fracas when Vietnamese forces consisted chiefly of lightly armed militiamen.

"Before, they used sticks and fists and stones," said Rei Yongsheng, a border official. "Now all they use is big guns."

The month-long war and lingering violence have taken a heavy toll on the peasants who have lived along Friendship Pass for generations, eking out a meager livelihood from the terraced rice fields.

Hundreds of families have been driven from their thatched roof huts into large community caves miles away. In some villages, only the men have stayed behind to tend the fields, often working under the cover of Army units.

The country roads linking the once-peaceful villages now carry signs of war. Mountains girding the road are pitted with body-sized cavities dug out by local militiamen to provide temporary, individual bomb shelters for passers-by in times of shellings.

A few miles from Friendship Pass, a roadside Martyrs' Cemetery holds hundreds of soldiers killed in the 1979 fighting, their gravestones etched in the honorary color of red.

In one still functioning border community named Ban Jun, villagers said they endured five days of Vietnamese mortar fire during the November harvest. tCramming into an unlit, poorly ventilated tunnel, they waited for hours at a time while Chinese troops wheeled heavy artillery to the border and returned the fire.

Six villagers were said to have been seriously wounded during the bombings. One enemy shell landed on the roof of a newly built elementary school, leaving a gaping hole and shattering the glass windows. Fragments of mortar bearing the Cyrillic lettering of the Soviet Union, Vietnam's chief ally and arms supplier, still cluttered the village square.

For the simple border people in villages like Ban Jun, Peking's abrupt shift from amity to war with Hanoi in the late 1970's took some adjusting.

Nearly all of the Chinese border dwellers are members of the Zhuang minority, a large ethnic group similar in traditions and ancestry to the minority people living on the Vietnamese side. For decades the two peasant groups crossed freely into each other's communities, trading goods, intermarrying and even developing a border patois.

In Ban Jun, a new department store was built just before the war to accommodate the large number of Vietnamese who entered China every day to shop.

The department store never opened and Ban Jun has become a strategically important border outpost linked to Vietnam by a dirt path known as Narrow Pass. More than 600 soldiers guard the pass and adjacent villages, curiously contrasting to the pastoral character of Ban Jun, where hogs roam freely nibbling at sweet potato vines left for them on country roads.

In a two-story white building that once housed meetings for Chinese and Vietnamese village bosses, soldiers armed with automatic weapons anxiously watch for enemy movements in the tall grass covering the path. On the walls, the guards have scrawled patriotic poems, pledging to sacrifice their lives for Ban Jun's defense.

The scrappy villagers who remain in Ban Jun to till the fields speak bitterly of their old neighbors today, holding that Vietnam owes them gratitude -- not bombs -- for China's help in the war against American troops supporting the South Vietnamese government in Saigon.

"The Vietnamese ingrates take your good and return you evil," said Zhou Zitan, a 26-year-old rice farmer who stayed in Ban Jun after moving his wife and child to a cave.

Despite the recent heating up of border tensions and war of words between Peking and Hanoi, Western defense analysts are betting against another Chinese "lesson" in Vietnam. The costs are too high in lives, precious economic development dollars and diplomatic prestige, especially since Vietnam has beefed up its regular Army forces on the border and gained clear superiority in equipment, according to the experts.

But in Ban Jun and other Chinese border communities near Friendship Pass, there is a unanimous cry for a "second lesson."

"The enemy seems to have learned little from the first lesson," said Li Baofu, the commanding officer at Narrow Pass. "We must make a second lesson stick."