Washington — Three years after the peak of the Indochinese refugee crisis, the flow of refugees has ebbed substantially.
The wars, poverty, and oppression that have forced more than 1 million Indochinese to flee since 1978 have not abated. But efforts by Western and Asian governments to discourage the refugee flow are beginning to have an effect.
Indochinese refugee arrivals in the non-communist countries of Southeast Asia during May and June declined by half compared to the same period last year. Since October 1981, the refugee population in the region has dropped from 265, 000 to 237,000 -- due to the limited resettlement that is still going on.
Ironically, the tougher approach of countries receiving refugees may leave Thailand -- which has instituted and encouraged many of the policy changes -- with tens of thousands of refugees with no place to go.
Indochinese refugees arriving in countries throughout Southeast Asia are discovering that resettlement opportunities in the West are being closed off and that they may be forced to spend years in barbed-wire camps.
Among the steps taken to discourage refugees:
* The United States and Australia, in effect, are limiting admissions to those refugees who can prove they have direct ties entitling them to resettlement. The two countries also require refugees to prove they face persecution in their homelands.
* Thailand is interning Vietnamese and Laotian refugees under a policy called ''humane deterrence,'' which prevents them from even applying for resettlement abroad.
* Hong Kong, which until recently allowed Vietnamese boat people to find employment while living in open camps, is now confining new arrivals to a remote island in the territory's harbor.
US State Department officials and diplomats from some Southeast Asian countries say they are satisfied with the initial results of the new policy initiatives.
A Malaysian diplomat says that with fewer than 10,000 boat people now in Malaysian camps, the refugee question ''is not the burning issue it was before.'' He says Malaysia has received private assurances from the US that, despite the new guidelines, the refugees would eventually be resettled.
But Thailand, which has three-quarters of all the refugees in Southeast Asia, may face a substantial residual problem. Recently, Thai officials have been expressing dissatisfaction with the Western commitment to reduce Thailand's refugee burden.
In a speech last month in Bangkok, the highest-ranking Thai refugee official, Air Force squadron leader Prasong Soonsiri, said that ''Thailand is determined not to allow even one displaced person (refugee) left on her soil.''
''If all countries and international organizations fail to honor their commitments,'' he said, ''and Thailand has to bear these grave burdens alone, I deem it necessary for Thailand to take a new step in order that our interests and security can properly be preserved. It is unavoidable for us to be concerned with the prevailing situation when many third countries have adopted new policies to accept fewer displaced persons for resettlement. They claim that they have done enough; therefore, we can say likewise that we in Thailand have done more than enough.''
Although Prasong did not single out a particular country in his speech, in an interview another high-ranking Thai official criticized the US for reducing its monthly Indochinese refugee admissions. In the last year, the Reagan administration and Congress have reduced refugee quotas so admissions now average fewer than 7,000 each month, compared to 16,000 in 1980.
Thailand is caught in a bind partly of its own making. Under its ''humane deterrence'' policy, many refugees are excluded from resettlement. And with the tighter immigration standards in the West -- standards that Thailand originally urged these countries to adopt -- other avenues are being closed off.
Because the refugee population is not being reduced fast enough, there are strong political pressures in Thailand to act unilaterally to reduce the refugee burden.
The high-ranking Thai diplomat said Thailand may pursue the option of encouraging ''voluntary relocation,'' whereby Kampucheans will leave the refugee camps and return to the Thai-Kampuchean border.
In a recent interview, Eugene Douglas, State Department coordinator for refugee affairs, said that US officials are obligated to admit only those refugees who ''have established claims to refugee status and are admissible'' under US law. Still, he said that Kampuchean admission decisions ''are open to review.''