Thai Army units today fired hundreds of mortar rounds into a squalid camp containing about 60,000 Cambodian refugees, killing dozens of them, journalists who visited the camp said.

Situated close to the Thai-Cambodian border, Camp 511 was operated by right-wing Khmer Serei guerrillas who had clashed with Thai troops in recent days.

A Khmer Serei officer said late today that 93 civilians and six soldiers had died in the shelling.

Rosalynn Carter, who arrived in Thailand Thursday night on a 40-hour visit to observe and publicize the plight of Indochinese refugees, visited another refugee amp about 45 miles from Camp 511 early Friday, news services reported.

"I can only say I want to go home as fast as I can and mobilize and do all we can to help the people here," the first lady said.

It was not known whether Mrs. Carter had been told of the shelling of the refugee camp.On her arrival here she said; "Thailand's compassionate and courageous response to the staggering human misery of its neighbors has meant life for thousands upon thousands of people. We owe Thailand not only our admiration but also our full support, which I pledge to you here tonight."

In response, Thai Prime Minister Kriangsak Chamanan said: "We in Thailand, and other like-minded countries of this region, are determined no longer to be bamboo bending with the wind. We shall take a firm stand on basic principles that should govern relations not only between states, but also fellow human beings."

Assistant Secretary of State Richard Holbrooke, traveling with Mrs. Carter, said of today's shelling, "We are concerned. It illustrates the tremendous danger that exists on that border." He said the United States would press Thailand to provide medical support to the wounded.

It remained a mystery why the Thais attacked the refugees, who had sought haven in Thailand after a decade of warring and hostility in Cambodia that climaxed with Vietnam's invasion of that country a year ago.

But the Thai military is known to have grown distrustful of the poorly disciplined bands of Khmer Serei guerrillas. There are some six separate and feuding groups that have sprung up along the Thai border and emerged as a minor third force in the Cambodian conflict.

The Thai Supreme Command recently reported a clash with "foreign soldiers" believed to be Khmer Serei.

Thursday, according to Cambodians whom the journalists interviewed, two Cambodian women were kidnaped and raped. Khmer Serei soldiers blamed Thai soldiers and this morning sent three armed men out to meet them. The Cambodians were arrested. More Cambodians came out, and small-arms fire broke out. After that, the Thais reportedly called in mortar shelling.

The shelling began about 10 a.m. and continued until 4 p.m.

" it was pandemonium, people running and screaming," said John Gudjohnsen, a cameraman for WFAA-TV in Dallas. His crew and other American journalists were by chance just outside 511 when the shooting began. They later entered the camp for 45 minutes and counted 28 heavy shells landing in and around it.

Another American in the group told of seeing a woman in her mid-twenties wounded in the back of the head. Her husband and son crouched in a fox-hole nearby.

"Mother is dead, my mother is dead," the boy, about 7, whimpered.

An old woman wandered in a daze, muttering, "Five, six years and it never stops. It goes on and on, when will it stop"?

Shells hit the annex of the camp's clinic and set it afire, the American said. People gathered about 10 wounded in one place. A medic shouted for iodine as he sheared away the hair of a man's head..

The journalists said it appeared many of the wounded would die for lack of medical care. They said they saw six bodies.

As people fled into the jungle, the Americans said, the shelling followed them. Gudjohnsen said that throughout the shelling a spotter plane flew over the area at about 2,000 feet, sometimes firing shells that exploded in smoke, apparently to mark targets. The journalists took compass fixes on the sounds of the shells and said all were coming from Thai territory.

Later the Americans spoke with Thai soldiers who, they said, admitted their side had done the shooting. People in a nearby village said that Thai mortar crews there had been active in the morning.

Officials traveling with Mrs. Carter's party tonight viewed film shot by the U.S. television crew.

In the past, diplomats have often said Thailand tolerated and perhaps encouraged the Khmer Serei presence as a buffer against the Vietnamese who are in Cambodia supporting the Heng Samrin government. Thailand recognizes Pol Pot's Khmer Rouge which together with the Khmer Serei are fighting the Vietnamese.

The Khmer Serei groups exercise a warlord-like sway over jungle and farmland that straddles the Thai border. Camp 511 was headquarters for several hundred soldiers calling themselves the National Movement for the Liberation of Kampuchea (Cambodia). Unlike other Khmer Serei groups it is aligned with Prince Norodom Sihanouk, the former Cambodian head of state who now lives in Peking.

Over the months 511 and camps like it have attracted huge numbers of Cambodians in search of food and safety. By one estimate there are 250,000 people in the camps. Khmer Serei officers say they are on the Thai side of the border although Thailand, which is officially neutral in the Cambodian conflict, contends they are in Cambodia.

In recent weeks the Thais announced plans to move most of the camp's civilians to more permanent quarters deep inside Thailand. The Khmer Serei, however, are not happy with the prospect of losing their population base.

Last week Thai troops moved to close down black markets at which Cambodians buy rice, clothes and other necessities. It was apparently an effort to make a move elsewhere seem more attractive.