The two teenaged Cambodian brothers, who have stuck together through years of war, famine and brutal government, were visibly elated when their bus sped past bags of rice stacked 10 feet high.

A few minutes before, riding toward a new United Nations refugee camp here, Kut Mon and Kut Suvan had asked if there would be a lot of rice. Passing into the camp and seeing a mountain of supplies was dramatic proof that the threat of starvation was finally behind them.

Arrival at Khao I Dang also placed them beyond the reach of all three of Cambodia's warring factions: the deposed Khmer Rouge, the Vietnamese- sponsored Heng Samrin government now in Phhom Penh, and a collection of right-wing Khmer Serei (Free Khmer) groups.

In the past 12 months the boys have lived under -- and escaped from -- all three factions, most recently the Khmer Serei. Now Mon and Suvan apappear to have had enough of Cambodia. "We'd go to the U.S., or France, or any country that would take us," said Suvan.

Ten days ago, the Thai government announced plans to build camps well inside Thailand and fill them with the estimated 560,000 refugees camped out on both sides of the Cambodian frontier. Most of them, as Mon and Suvan did, live in enormous settlements of thatch and plastic sheeting houses, operated by Khmer Serei groups and vulnerable to mortar fire from Cambodia.

The two brothers and 40 other refugees on the bus were among the first to leave the border area. On the highway they were awed by the wealth they saw -- motorbikes, lush planted fields, modern houses. Parents held small children up to windows. "All the roads in Cambodia are potholed and muddy," volunteered Mon. "There are no vehicles either -- the Khmer Rouge took them all away."

Under a late afternoon sun, the bus pulled into Khao I Dang, where bulldozers, medical workers and laborers are working overtime to make places for 200,000 people. The boys alighted at a white hospital tent and got a quick medical exam. Neither was seriously ill, but they, like everyone else, obediently gulped down large white pills to counter malaria, the most dangerous disease among Cambodian refugees.

As day gave way to twilight, the boys were awaiting cooking pots and plastic and bamboo to fashion into a shelter. They asked after an older brother they believed had arrived earlier. Both parents were dead, they said; their father was executed by the Khmer Rouge in 1976.

Mon and Suvan, aged 17 and 18, seemed to think little of the enormous risks they had taken to reach Khao I Dang. Like almost everyone in Cambodia, they had endured unspeakable hardships since the Khmer Rouge captured Phnom Penh n 1975.

First came four years of farm work on a Khmer Rouge commune. Then last December Vietnamese troops invaded Cambodia to install the Heng Samrin government. The boys' commune was overrun and the Khmer Roughe chased out. As food shortages increased in the following months, Mon and Suvan decided, like hundreds of thousands of their country men, to break for the Thai border.

They dodged Vietnamese patrols and other dangers: "Just walking along forest paths you risked stepping on mines." Suvan said Six weeks ago they arrived on foot at Camp 204, where perhaps 200,000 people have built huts in disputed frontier territory.

The ill-disciplined Khmer Serei group in charge calls itself the National Liberation Movement of Cambodia and talks of driving both the Khmer Rouge and the Vietnamese from Cambodia.

In the first weeks, the boys probably saw 204's soldiers as protectors. Their camp had food and people were generally free to lead their own lives.Suvan took to wearing Buddhist amulets for good luck, a custom suppressed with all religion -- by the Khmer Rouge.

But when the Thai authorities announced plans for the move, the Khmer Serei became captors. Their leaders feared international rice shipments would stop and their newly founded Liberation Movement would collapse if the civilians departed.

Soldiers at 204 were ordered to stop anyone trying to reach buses the United Nations sent to wait in a nearby Thai village. (At other Khmer Serei settlements, however, soldiers allowed people to leave if they paid a fee.)

But last Friday Non Suvan cut through the jungle and once again eluded hostile soldiers. At about 4 p.m. they boarded the bus. "We felt extremely thankful," Suvan said. Only 200 people got out Friday: the U.N. had hoped to move 5,000 a day.

The boys escaped as the Khmer Serei heightened their campaign against relocation. Last Thursday soldiers shot and wounded a man trying to leave 204 and threatened to kill a U.N. interpreter, official sources said. On Friday the camp's leaders called a demonstration to protest "the politics of evacuation."

About 5,000 people, perhaps half of them children, waved banners made from discarded rice bags and cheered a collection of speakers.

"If the United Nations take us all away, there will be only Vietnamese left on Cambodian soil," said one officer with a pistol on his belt. Camp leaders claim that not a single person wants to go and that if anyone should change his mind he would be free to leave.

Conversations inside 204 during the demonstration indicated that few people had any interest in the Khmer Serei's struggle. (Given the rightist soldiers' problems in manpower, weaponry and discipline, few military analysts consider them a significant force on the battlefield.)

One woman in the late stages of pregnancy said soldiers had told her to stay put. "I'd like to leave with you," she told a reporter outside her thatched hut. "There are lots of medicines and food at the new camp."

As of tonight, 24,000 people had moved to Khao I Dang; 60,000 were supposed to have arrived. Official sources said the Thai military, which is determined to deny Vietnamese forces the tempting target the civilians would make, was planning to "break the logjam." Tactics might involve starving out the camp or forcibly disarming the Khmer Serei.

Camp 204's leaders are considered by many to be incapable of calm discussion. The commander is said to be a former timber smuggler. One of his lieutenants, who claims to be Cambodian royalty, pounds tables and bellows at visitors when he gets excited. Some refugee workers fear that Thai intervention could cause considerable bloodshed.