Thousands of Vietnamese troops with heavy weapons were pouring north toward this Vietnamese town near the Chinese border today, promising a likely major clash with Chinese invaders in the near future.

A deathly calm reigned in Lang Son itself. The town has been evacuated but there was an impressive marshalling of forces by the Chinese and Vietnamese sides as they apparently prepared for a major battle.

I saw thousands of soldiers, both regulars and regional troops, marching to the front, accompanied by trucks pulling 105mm artillery pieces brought from Dong Mo, miles from the border. Lang Son is only 12 miles from the border.

Heavy 130mm artillery dug in south of Lang Son was raining heavy shells in the direction of China today. To the rear, the Vietnamese have set up antiaircraft batteries.

The advancing troops passed by long processions of civilians going away from the fighting. The road was cluttered with army convoys carrying men, arms, munitions, fuel and supplies.

The commander of the Lang Son military region, Col. Le Son, said the Chinese were also regrouping and bringing up reinforcements, mainly at Dong Dang and Yenkhoai, three miles inside Vietnam.

"We think that once they have regrouped, they will try to surround us," said the colonel.

On the ground, the military situation appeared confused. The mountainous terrain gave a jigsaw look to the front, with the Chinese holding one hill and the Vietnamese another.

It was impossible to go closer than nine miles to the front, but in the noman's land being pounded by Vietnamese artillery, Chinese-held hills could be seen. They were marked by the Yellowish horizontal lines of their freshly dug trenches.

Vietnamese officials said Lang Son was evacuated starting Saturday night in an orderly and disciplined fashion. Today there was no sign of civilian activity in the town.