Two members of the U.S. Congress, allowed a brief look at the Sino-Vietnamese border war, said tonight that fighting there was "fairly fierce" and that "a great number of Vietnamese troops" were moving toward one part of the front.

Rep. Elizabeth Holtzman (D-N.Y.) said the strategic border town of Langson was "like a ghost town" when she visited it Thursday. Before leaving Hanoi this morning, she was told the town had not yet fallen to the invading Chinese army, but that "fighting was continuing on a heated basis" nearby.

Rep. Billy Lee Evans (D-Ga.) said he saw "very heavy shelling by the Chinese of Vietnamese positions" yesterday at Camduong, southwest of the Vietnamese border town of Laocai. The Chinese reportedly have taken Loacai and Evans said he had the impression they were trying to press farther. His Vietnamese guides took him back to Hanoi, a 12-hour jeep ride after "one shell hit near where we were."

The accounts by Holtzman and Evans at joint press conferences in Bangkok and again here appeared to support reports by Western analysts that fighting is concentrating at Langson and Laocai. The two towns mark the border access to the two most important road and rail routes to the Vietnamese capital of Hanoi, about 100 miles southwest of Langson and about 150 miles southeast of Laocai.

But because of only fragmentary battle reports and the lack of official information from Peking, it was still impossible to determine whether China intends to prolong its invasion or try to push more deeply into Vietnamese territory. The few on-the-scene accounts indicated that the Chinese have mounted a major artillery barrage. There was no way to tell, however, whether the shelling was preparation for more movement forward, or just to punish the Vietnamese and discourage resistance.

Holtzman and Evans arrived in Hanoi on Wednesday to seek Vietnamese cooperation in stopping the flow of refugees out of Vietnam in dangerous small boats.Holtzmen said only that her delegation received a "positive response" to their requests on refugees, and then went on to discuss the border war.

"I don't think the Vietnamese really know how long the fighting will go on," she said. "But they are very confident." She said there was a danger the war could escalate to a wider conflict, particularly if the Soviet Union intervened on behalf of Vietnam. She suggested to reporters fthat U.S. recognition of the Hanoi government might help speed diplomatic contacts that could bring a solution to the conflict.

Holtzman said Vietnamese Vice Foreign Minister Phan Hien told them a new "domino theory" was in effect with China aiming to take all Southeast Asia. The official Chinese press, too, has recently accused Hanoi, in cooperation with Moscow, of seeking to conquer Southeast Asia and reviving the domino theory, once used by Americans warning of communist domination of the area.

Holtzman said when she visited Langson, "The city wass evacuated, doors padlocked. The civilian government had moved out two or three hours before we got there."

She said she saw artillery craters and buildings that had been hit.

"Thousands and thousands of Vietnamese citizens were on the road, taking with them their pigs and cattle and sometimes horses, and some carrying all their belongings on the back of a bicycle or on a pole," she said.

I would say we saw well over 5,000 refugees in just this one area. The strange thing is when you got a few kilometers south of Langson, you saw people working in their fields. I saw soldiers swimming in a river.

"If someone plunked you down in the middle of Hanoi, you'd have no sense there was a war going on less than 200 miles away."

In a battle report today, Radio Hanoi departed from its usual practice by giving no specific figure for Chinese casualties. It simply said "hundreds" of Chinese troops have been killed or wounded and 73 military vehicles destroyed yesterday.

The radio said a batallion of Chinese troops was "badly trounced" east of Langson and "hundreds" of Chinese were killed or wounded in Langson Province. The radio also said Vietnamese forces had smashed a Chinese column on Highway Four between Dongkhe and Caobang, at 18 miles inside Vietnam the deepest reported penetration of Chinese troops.

Following its practice throughout the eight-day-old war, Peking gave no casualty report tonight. But the official New China News Agency did report the U.N. Security Council meeting on the situation in Southeast Asia, quoting U.S. Ambassador Andrew Young's call for a cease-fire and withdrawal of foreign forces from Vietnam and Cambodia.

Chinese officials in Peking have said the invasion will be limited in time and scope, and will end when the Vietnamese have been punished sufficiently for previous border raids. No limit has been set, however. Official Peking statements suggest an effort to win a withdrawal of Vietnamese troops from Cambodia, where pro-Chinese guerrillas are fighting, before the Chinese troops would leave Vietnam.

[In Tokyo, the Japanese news service Kyodo reported from Peking that Chinese officials are saying they have not completed their "punishment" of Vietnam. One Chinese official was quoted as saying that whenever China does withdraw its forces it will pull them back to a border defined by China and not by Vietnam, Kyodo reported. The official said that China will establish a new border with Vietnam. Kyodo said this is the first time Chinese officials have mentioned establishing a new border after the fighting is over.]

Roy Jenkins, president of the European Economic Community Commission, said Chairman Hua Kuo-feng told him in Peking today that the Chinese had calculated all risks, including possible Soviet intervention, before deciding to launch their operation against Vietnam. Jenkins, at a news conference shortly after his meeting with Hua, said Hua described the operation as limited but did not elaborate on China's intentions.

A radio report by the pro-Peking Khmer Rouge guerrillas, believed broadcasting from southern China, said more than 200 Vietnamese troops in central and western Cambodia were killed or wounded in recent days. Analysts here and in Bangkok said they had no reliable reports yet of any move of Vietnamese troops from Cambodia to join the conflict on the Chinese border.

Radio Hanoi acknowledged heavy fighting near Laocai, the northwest border town reported taken by the Chinese. It said Chinese troops backed by tanks and artillery launched a new attack Friday. Evans said he saw no Vietnamese tanks when he visited the area, but heard an artillery barrage that lasted 45 seconds. Evans said this meant "there were several hundred guns firing right after another."

Washington analysts have suggested the fighting along the border is not as intense as has been reported by analysts monitoring radios and other intelligence devices in the area. They have also expressed doubt about reports that large numbers of regular Vietnamese Army troops have joined the fighting, which in the first days at least was waged mostly by militia forces.

Bangkok analysts have said the 30,000 to 50,000 main force troops near Hanoi and Haiphong appear to have kept their positions, but that troops from unattached regiments farther south, and perhaps from Laos, are moving toward the border area. Observers inside the country have said Vietnamese militia and regional forces appear to be well armed with good fortifications.

Holtzman and Evans said they saw two Soviet transport aircraft at Hanoi's airport this morning, but were not told if the planes had brought in war supplies. Bangkok analysts have reported a Soviet airlift under way. The Soviet Pacific Fleet flagship, the cruiser Admiral Senyavin, with sophisticated surveillance equipment, was reported by Japanese sources to be patrolling with a Soviet destroyer off the East China coast about halfway between Shanghai and the Japanese island of Kyushu.