Vietnamese forces captured part of a Cambodian resistance camp today in a second day of fighting near the Thai-Cambodian border that has forced nearly 20,000 civilians into a precarious no man's land, according to Thai military sources and western relief officials.

The Vietnamese attack launched yesterday against the Nong Chan camp run by the noncommunist Khmer People's National Liberation Front resumed at dawn today with an artillery barrage and infantry assaults, a spokesman for the front said. He said that while the civilian population of more than 20,000 had been evacuated, about 1,000 of the front's guerrillas, led by camp commander Chea Chut, were still holding out against roughly 2,000 Vietnamese attackers.

[In Washington, the State Department issued a statement condemning the attack on Nong Chan and urging Vietnam "to reconsider its failed policy of military conquest and allow the Cambodian people to rebuild their country free from outside interference."]

Thai military sources and western diplomats said the Vietnamese took over part of the camp today, but could not confirm reports from the border that 22 persons had been killed and 100 wounded.

A western relief official said 34 wounded Cambodians had been evacuated to a hospital inside Thailand. A Cambodian guerrilla spokesman said he had reports of only four resistance fighters killed and 18 wounded in the battle.

According to a U.N. relief offical, a potentially serious problem lay in the inability of relief organizations to reach nearly 20,000 Cambodian civilians who evacuated the camp yesterday but were being kept by Nong Chan camp authorities on Cambodian soil a few hundred yards southwest of the camp. It is located about 18 miles northeast of the Thai border town of Aranyaprathet.

About 1,000 Cambodian refugees reached an evacuation site on Thai soil, and others were headed north toward the crowded resistance settlement of Nong Samet. Also run by the Khmer People's National Liberation Front, the Nong Samet camp shelters about 60,000 Cambodian refugees and is as vulnerable to Vietnamese attack as the Nong Chan settlement.

With approximately 12,000 guerrillas, the front is the largest noncommunist resistance faction battling the nearly six-year-old Vietnamese occupation of Cambodia. The communist Khmer Rouge, with 30,000 to 40,000 guerrillas, bears the brunt of the fighting against Hanoi's 160,000 to 180,000 troops. Both resistance groups are partners in an uneasy, U.N.-recognized coalition government with a smaller noncommunist faction led by Prince Norodom Sihanouk.

While the Khmer front appears to be the main target of the current Vietnamese activity, there have been unconfirmed reports that Khmer Rouge positions have come under shelling about 25 miles south of Aranyaprathet.

Bangkok newspapers reported that Thai Army gunners opposite the Nong Chan camp and the Khmer Rouge positions were returning artillery fire when Vietnamese shells landed on Thai territory.

A Thai Army spokesman said Thai troops along the border have been placed on full alert since the attack on Nong Chan began yesterday.