The populations of many of Southeast Asia's once teeming refugee camps are dwindling as Western countries appear to be making good on resettlement promises.

But knowledgeable sources privately fear the government of Vietnam may soon lift its moratorium on departures, touching off a new exodus this year that will more than fill existing camps and create hundreds of new ones.

"There are about a half million people in Vietnam just waiting to take off and go elsewhere. Many have bought their tickets and are ready to get on a boat. The whole thing is about to blow up all over again just like last year," one source said. Some boatloads have already appeared.

The trickle of Vietnamese that had been fleeing since the communist takeover in 1975 suddenly turned into a flood last summer, swamping Southeast Asian countries such as Indonesia, Malaysia and Thailand. Government officials in the region charged the move was a deliberate attempt by Vietnam to undermine the stability of the region.

Reacting to charges, Hanoi pledged during a conference in Geneva last July "to make every effort to stop the illegal departures . . . for a reasonable period of time."

Indeed the flow of boat people has ebbed since last summer, but not before 314,000 had washed up on Southeast Asia's shores, boosting the total numbers of self-exiled Indochinese to more than 540,000.

With the influx slowed, Western countries that promised at the Geneva conference to boost resettlement efforts and quotas have managed to make a big dent in the camp populations.

Statistics released by the U.S. Refugee Program reveal the receiving countries have taken 262,263 -- nearly half of the refugees who survived harrowing journeys to other Asian countries between August 1977 and the middle of January.

The lion's share, 148,764, has been accepted by the United States and another 62,693 have been scheduled for transfer to American soil.

"We're really rolling now," said Lance Downing, a member of the U.S. Refugee Program team based in Singapore, after a return visit to camps in Indonesia's remote Anambas Islands. His last visit to the area was last August.

"Things have improved greatly. A lot of international groups have gotten involved helping out," he said.

The number of boat people here in Indonesia had been reduced by Feb. 1 to 29,808 from cumulative arrivals of 54,512.

Just last August, U.S. and Indonesian officials were worried many of those stranded in the Anambas might not survive the current rainy season, because of the difficulty getting supplies to the small rugged islands.

But Downing said ships from West Germany, the Netherlands and the United States have managed to transfer the bulk of the Anambas boat people to safer ground on Galang Island, closer to Singapore. The next stop for most will be the United States.

Now, less than 10,000 remain at the Air Raya and Kuku camps in the Anambas compared to a combined population last August of nearly 32,000.

During a recent stop at Galang, Downing said he was encouraged by the morale of the refugees. "They can see great numbers being moved out every day. I think they are pretty optimistic," he said.

The Indonesian government is reportedly "quite pleased," although foreign ministry spokesman S.A.M. Alaydrus said, "We had been told about 5,000 a month would leave, but they have not reached that level."

More dramatic progress has been made in Malaysia, which last year closed off its waters to leaky boats packed with people. Its navy even started pushing those who landed back out to sea.

As of mid-January, the refugee camp population of Malaysia had dwindled to 32,644 from cumulative arrivals of 123,094 Indochinese. The plywood and chicken-wire shelters of Pulau Bidong once housed 45,000. Now only about 15,000 remain and overcrowding has eased.

Abdul Manaf Hamid, a spokesman for the Malaysian government, said officials in Kuala Lumpur were quite satisfied with the response to demands that the boat people be moved. But he too said the pace should be speeded up.

Inroads have also been made in Hong Kong, where more than 82,000 arrivals from Indochina taxed a tiny colony already swarming with 5 million of its own people and a steady influx of illegal immigrants from neighboring China.

The U.S. Refugee Program statistics show 27,330 boat people have departed for new homes in the West.

Problems continue, however, in beleaguered Thailand. Relief programs have managed to place 104,101 Indochinese in permanent homes in other countries. About 14,000 still inhabit a string of camps.

Those figures are deceiving. The U.S. Refugee Program estimates do not include about 125,000 Cambodians in holding camps along the border. Another 200,000 refugees are thought to be in Thailand, but have not been formally identified as refugees by either the United Nations High Commissioner for Refugees or the U.S. program.

Small numbers of refugees still remain in the Philippines, Singapore, Taiwan, South Korea and Japan.

Besides the United States, other countries that have resettled large numbers of Indochinese refugees include France with about 60,000 and offers for another 22,600; Canada with about 36,000 and offers for at least 36,000 more and Austrailia which has taken more than 33,000 and has offered places to another 14,000 thus far.

U.S. Refugee Program regional coordinator James Schill said about 14,000 refugees are leaving each month for the United States. California has by far the largest number, more than 120,000, according to program statistics.

Schill attributed the faster pace of resettlement to the huge exodus last summer when "the profile, the high visibility, the death and destruction that was so high and was so well reported." He said he expects the pace to continue at least through the end of the year because of commitments that have yet to be fulfilled.

There is concern, however, that no matter how many refugees are resettled, a number of homeless will remain unclaimed, including the aged and the unskilled.

Schill also admitted that the fact that Western countries have opened their doors to large numbers of Indochinese land and boat people provides a great incentive for those still wishing to leave Vietnam. "There is no question about it," he said.

The sources warned that there are signs that a new wave of refugees may have already begun. Recently, many Asian newspapers ran an Associated Press picture of the USS San Jose rescuing 55 Vietnamese from a rickety wooden ship in the South China Sea.

And the U.S. coordinator for refugees, Victor Palmieri, caught a first-hand look at the problem when a boatload of about 90 refugees came ashore while he was touring the Anambas Islands with U.S. Ambassador to Indonesia Edward A. Masters.

Some 250 to 300 boat people landed in Indonesia last month, a sharp upsurge in arrivals.

Some sources believe the government of Vietnam will lift its moratorium shortly and boats will come in even greater numbers than last year.