In the closing months of World War II, the British and Americans forcibly returned to the Soviet Union thousands of Russians who had fought on the German side. Most were not conscious traitors, but had been impressed into service or simply caught up "in a vast human convulsion few of them understood," as Paul Johnson wrote in "Modern Times." In the correct surmise that they were being sent to their deaths, many became hysterical, rioted and attempted suicide. It took years for the enormity of this injustice to sink in among Westerners. Looking back, we wonder how on earth it could have been allowed to happen. The answer seems to be a combination of bureaucratic rigidity and a failure of empathetic understanding.

The Cubans from the 1980 Mariel boat lift who are now rioting in federal prisons don't face summary execution or death by starvation if the administration is able to proceed with its plan to send them back. However, they evidently feel that what they do face in Cuba is worse than what they face here in the United States, which is permanent incarceration. Who would wish to say they are wrong? Of course most of them are genuine lowlifes. On the other hand, we don't have the excuse of the chaos and necessary callousness of wartime to help explain a moral miscalculation.

The bureaucratic case for sending these people back to Cuba, if Fidel is willing to take them, is impeccable. As aliens who were apprehended at their point of entry into the United States, and then let in anyway on "parole," they are not merely "illegal" (like people who sneak into the country and then are captured) but "excludable." The courts have held that excludable aliens, unlike mere illegals, are not "persons" under the Constitution and therefore have no rights at all except those the government chooses to grant. If they could have been kept out in the first place, as criminals and the mentally ill may be kept out, they can be summarily deported. If they commit crimes in this country, ditto.

Castro surely played a dirty trick by unloading the wretched refuse of his prisons and mental hospitals onto the "freedom flotilla" in Mariel harbor. Nevertheless, it is dawning on Americans, apparently including the Reagan administration, that our treatment of these people has been unbelievably callous. The callousness starts with the eery dismissive group description, "criminals and mental patients," with its totalitarian overtones. Since when does the United States lump together criminals and mental patients, as if they formed some common class, civilization's subhuman waste product? Hitler thought that. We don't.

In fact, at least a few of the Marielitos we want to ship back are poor mental defectives who have never committed any crime. According to the American Civil Liberties Union, there are more than 100 Marielitos in St. Elizabeths Hospital. Some were committed after violating the law in this country, but some were committed just because they're sick, and others have been hospitalized since they arrived in 1980.

Many on the deportation list have been convicted of minor offenses, such as possession of a small amount of marijuana. This may disqualify them to sit on the U.S. Supreme Court. But is life imprisonment in a communist society suitable punishment for this crime -- or for no crime at all?

Even the serious criminals among the Marielitos have been treated in a way that actually deserves the hackneyed adjective Kafkaesque. A couple hundred have been jailed in America without trial since 1980 because of criminal records in Cuba. Do you suppose they got their Miranda warnings? Thousands have been convicted and jailed for crimes in this country, served their time, been duly released, and then immediately reimprisoned indefinitely to await the outcome of negotiations with Castro. Others are back with their families or in halfway houses, but are subject to rearrest and/or deportation at any time. The list of 2,500 people Castro has agreed to take back (out of about 10,000 potentially eligible) is classified! No one knows who's on it, including those who are.

The Mariel episode was Castro's ingenious way of calling America's bluff. It's forgotten now that the American government objected not just to the arrival of "criminals and mental patients" but, after a few days, to the whole flood -- which was stemmed, much to our relief, at 125,000, surely a small fraction of those who would actually like out. The United States is happy to welcome the odd concert pianist or nuclear physicist who escapes from a communist nation. But our regular (and, of course, justified) condemnations of totalitarian regimes for refusing to let their people exit are somewhat hollow, since we would never let them enter in unlimited numbers. What's the right to emigrate worth if there's no place to immigrate?

Of course, despite what it says on the Statue of Liberty, we can't really welcome all the world's wretched refuse. But when some of that refuse is swept our way by the tide, even "criminals and mental patients," we can't just sweep it back.