Children cry in their mothers' arms. Cheap plastic baggage is tossed atop buses and stowed. As well-wishers throng the gates of this refugee center, 114 Laotians are called to board buses for Bangkok, the last stop before resettlement in the United States and other countries.

Engines start up just after sundown and the allnight drive is under way. The scene is repeated often in Thailand's seven camps for Laotians: since 1975 over 140,000 Laotian refugees have left Thailand for other countries, U.N. figures show. About 105,000 are currently in the camps.

Although the Cambodian refugee exodus has seized the world's attention, the human flow from Laos also has achieved rates rarely matched in history.

Almost one-tenth of Laos' 3 million citizens have left since the communist Pathet Lao, with help from Vietnam, won its 20-year war against American-supported governments in Vientiane.

Swimming or bribing boat owners to run them across the Mekong River, which is the border, Laotians continue to make the short but dangerous trip. In September, over 1,700 newcomers were registered at U.N.-sponsored camps. i

Those who cross Laos' southern borders usually make for Ubon, a name well known in towns and villages across the river. Built orginally as a bomb depot for the U.S. Air Force, the camp now houses about 15,000 Loatian refugees.

Long rows of thatch and plywood homes have risen along the camp's concrete roads. There are dirt-floored coffee shops where old men play chess, a Buddhist temple with 15 monks, and makeshift photo studios.

Measured in terms of radios, motorbikes and consumer goods, the camp is far ahead of most district towns in Laos.

War and political oppression at home drive out many Laotians, in particular the Hmong hill people who fill refugee camps north of Ubon. These people, armed in the 1960s by the U.S. Central Intelligence Agency, are today the target of repeated suppression drives by the government if they stay in Laos.

Some of Ubon's people -- almost all are lowlanders -- left to avoid "seminar," the euphemism for political reeducation in remote camps. Since 1975, perhaps hundreds of thousands of people associated with the U.S.-supported government have been sent to seminar, where some die of hardships and hunger.

But many lowlanders leave more to escape unemployment and poverty than the Pathlet Lao. Once-bustling markets in provincial towns have fallen silent. Hasty collectivization has stagnated trade and production and eliminated many urban occupations, refugees say.

The case of a 61-year-old carpenter encountered in a Ubon coffee shop is typical of this group. He brought his family across the river in 1978 because "there was no work to do. The government had taken over everything."

Had he had trouble with the communist authorities or been sent to seminar, he was asked. The answer was no to both.

"They considered me too old to study politics," he said. "They thought I couldn't learn the new ways."

Elsewhere in Ubon one encounters farmers who say they left because they resented attempts to communize agriculture, and Chinese merchants who found their profits wiped out by state restrictions on private trade.

Some Thai and U.N. officials feel that people like these should be treated as emigrants, not refugees. They are not fleeing persecution based on ethnic origin or political belief, the officials contend, but rather they are simple seeking a more properous place to live.

News of resettlement programs -- more than 100,000 Laotians have entered the United States since 1975 -- and free rice in Ubon camp attract people from across the river who otherwise would have stayed home, it is argued.

"Half of Asia would move to the U.S. if given the chance," said one refugee official.

In 1977, the Thai government briefly attempted to give new arrivals an eligibility test to identify and eventually repatriate such "economic refugees." But the program was abandoned following reports that a number of Laotians sent back had been shot.

Many U.S. refugee workers believe that their government, because of its role in the Indochina war, has a responsibility toward any person who flees from Indochina. The U.S. Embassy in Bangkok has generally urged the Thai authorities to treat everyone as refugees.

Expanded resettlement quotas that followed the Geneva Conference on Refugees last year have helped make the Thais more tolerant. The United States accepted about 2,700 Indochinese refugees from Thai camps in June 1979. Last month the number was 7,500.

Interviewers keep a sharp eye for Thais posing as Laotians. Since language and culture are virtually identical on the two banks of the Mekong, refugees are questioned in detail to ascertain whether they are actually Laotians.

While resettlement is steadily clearing the camps, not everyone wants to go. "That's the big question for the Thais," said one refugee worker, "what to do with people who won't go to third countries."

Some are reluctant to leave the free food and slow pace of the refugee lifestyle. Others have businesses in the camps or are involved with anticommunist guerrillas operating across the river.

Officials in Bangkok continue to threaten that Laotians who decline resettlement elsewhere might be forcibly sent home. But for now, with the United Nations paying most of the camps' bills, and Thailand enjoying world praise for its hospitality to refugees, camps like Ubon appear to be secure.