'Tis the day before Christmas, and our president has done all that he can think of to remind us that this year our merriment ought to be restrained. He is lighting only one light on his Christmas tree. Rosalynn is shopping in discount stores.

Nonetheless, though criticism does not come easily to me, there is more our president might do to restrain our joy. He might tell us about Christmas in Cambodia and along the Thai border, where, though the journalists have moved on, the Cambodians still starve. Surely our president knows this. Stripped of most of their meager possessions, ravaged by pain and disease, enhaloed in a sadness that few Americans can even imagine, they pad silently and almost hopelessly through a desolate land.

These are not educated people. The educated were sacrificed months ago to further Pol Pot's procrustean essay into the Marxist mysteries. One-third to one-half of all Cambodians died then, and if, as the historians tell us, the English were set back when the flower of English manhood perished in the trenches of World War I, imagine what this hecatomb means for Cambodian civilization. Buddhist monks, professional people, civil servants, the bourgeois and all their diabolical agents -- perhaps 1 in 20 survived. Fifty-one Cambodian doctors remain to care for perhaps 4 million of their countrymen. Whole towns have had all vestiges of human life snuffed out. Before the fall of Phnom Penh, Western journalists liked to insinuate a decadent languorousness upon its citizens: they lolled about the cafes and the pools as the peasants huddled together terrorized by an unpopular war. Phnom Penh's decadently languorous are now dead. There are neighborhoods where not one human being has survived.

Until January 1979, this was the work of Pol Pot; since then the work has been taken up by yesteryear's proponents of peace and freedom, the glorious armies of Hanoi. Currently, they are coldly starving the remnants of the Cambodian nation. This is not a crime of passion. It is a very cold-blooded exercise in population control. As French journalist Oliver Todd noted last spring, the Vietnamese find too many Cambodians inconvenient. Thus thousands die every week. That is the Christmas story of 1979 whether the headlines note it or not.

In America, rights, so-called, are almost an obsession. Some even solemnize the rights of animals and trees. Out president has lectured the whole wide world on rights. Yet in Cambodia today one of the grisliest atrocities of the century is being perpetrated by a client wholly dependent on Papa Brezhnev's largness. Should not our president speak up? Secretary of State Cyrus Vance has told us that Papa Brezhnev shares with President Carter "similar dreams and aspirations about the most fundamental issues." Perhaps they could speak up together.

Imagine Christmas in Cambodia. Gathered around the tree is a family of six. Until April 1975 it was a family of nine, but three suffered savage extinction under Pol Pot's Utopia. Of the six that remain seated around the Christmas tree, four are starving and two of these pitiful creatures are near their death throes. The two who are not starving are both very hungry and probably sick. The only gift this family has this Christmas is a little bit of life. If our Cambodian family lives in the country's interior, it will dine on a broth made of boiled bark, roots and leaves.

It is, of course, difficult to envisage this horrible scene and to think of an American Santa Claus ho-ho-ho-ing somewhere offstage. Yet if you can get this far, perhaps you can go a step farther and envisage some of the heroes of 1969 intoning their popular chant: "Ho Ho Ho Chi Minh, the NLF Are Gonna Win." The rumor spreads that there exists today just one copy of the Tripitaka, the canonical text of Cambodian Buddhism. Cambodia is a dying country and a dead civilization. The NLF won.

One of the artifacts of an American Christmas is some gadget of dubious worth furiously hawked by the Madison Avenue wizards and raveningly purchased by the affluent citizenry. One remembers the Christmas of the electric toothbrush and the pet rock. 1979 seems to be the Christmas of the computer game. In Ban Nom Samet, the hot item this season is a sheet of blue plastic.

Ban Nom Samet is a refugee camp on the Thai border. There, a sheet of blue plastic affixed to four crude poles signifies a well-blessed home. International refugee agencies supply everything. The camp's 200,000 Cambodians have suffered extreme starvation. Some have ghastly infections on their bodies. The surgical table at the center of the camp is a sheet of plastic laid across the ground. For those modern cosmopolitan Americans who find children a nuisance, Ban Nom Samet is not without its charm. It has very few children and almost none between the ages of 1 and 5.

Right now, according to Leo Cherne, the tireless head of the International Rescue Committee, some 300,000 to 500,000 Cambodians are shuffling westward across the roads and fields of Cambodia to get to camps like Ban Nom Samet. They are driven by starvation and disease. It is not that Cambodia is completely without food. Actually, cities like Karpeng Sam probably have more food per capita than most other cities of the Third World. It is, rather, that the Vietnamese simply will not allow the food to be distributed. By late November, 22,619 tons of food had been sent by international relief agencies to Cambodia. Only 447 tons were distributed.

When will our president say something about this barbarism? Is this another one of those New Age diplomatic puzzles that is best left to the remarkable collection of subtle minds with which he has staffed the seventh floor of the State Department and the National Security Council? In Iran we cannot do anything; in Southeast Asia we cannot say anything.

The lesson of Cambodia is the lesson of the Nazi concentration camps and the Gulag. Some people are immune to Western principles of decency. A president who does not realize this and who believe that Papa Brezhnev shares fundamental aspirations with him ought to take in the sights of Ban Nom Samet, once he has retired.