AND STILL they come, refugees from the socialist "paradise" of Vietnam, braving the vengeance of their own government if they are caught while trying to flee, barbarous pirates and other hazards of the high seas, and all the uncertainties of life in a new land. Few of us may give the flow much thought any more. But from Vietnam and Vietnam-controlled Laos and Cambodia, some 49,000 people arrived by boat in nearby countries in the year ending Sept. 30 (down from 82,000), and 9,000 arrived by land in Thailand (down from 31,000).

The considerations impelling people to such desperation do not seem to have changed much since the communists took over in South Vietnam in 1975. They made life so miserable that a million of their citizens, not to speak of others from Laos and Cambodia, have taken the immense risks of illegal flight. There is now some legal migration under a United Nations program that sees to the "orderly departure" of about 1,000 Vietnamese a month. Some hope the program might be doubled. As welcome as it is, however, this program puts in the Hanoi government's hands the initiative in determining who departs.

In the receiving countries, an awkward debate has gone on for the last few years between those who would open the gates wide to all comers (mostly the gates to someone else's country) and those who would narrow the gates because of the costs entailed. To its credit, the United States has entered this debate as the country that has led the international effort to care for the refugees. It has admitted more of them to permanent residence than any other country, and it has accepted its responsibility to stir and help other countries to do their share.

The Reagan administration came to office as the first wave of American magnanimity was clearly peaking. To slow the flow, it cautiously put into practice a policy of "humane deterrence." The idea was to keep admitting deserving people but to spread the word, by the refugee grapevine and by international broadcasts, that neither in the nearby countries of first asylum nor in the United States and other resettlement countries would the welcome mat be out for those who do not face "severe persecution." Thus did American immigration officials begin last spring to apply more strictly the distinction made in the 1980 Refugee Act between political refugees and economic migrants; the latter were discouraged. Would-be immigrants were now required to show they had "demonstrably close links" with the United States.

One early result was a crisis in the first-asylum countries, whose readiness to accept new refugees depends on American readiness to guarantee resettlement for those already taken in. Thailand, for one, threatened to close its border. Fortunately, Attorney General William French Smith, visiting Thailand, recognized the arbitrariness of drawing a hard line between political refugees and economic migrants, and instructed the Immigration and Naturalization Service to apply a more humane standard in that and other categories. It should be going into effect now.

President Reagan is required by law to set an annual Indochina refugee ceiling. If the Smith standard is everywhere applied, then the United States should have little trouble going right up to the 64,000 figure he has set for 1983. In 1982, 73,000 were admitted (the ceiling was 100,000) and in 1981, 132,000 (168,000). Any number will always be somewhat arbitrary. Still, 64,000 will probably strike most people as respectable, not excessive. "Humane deterrence" cannot be allowed to become a catchword for the avoidance of American responsibility and leadership.