A sham battle of grandiose principles has divided the Carter administration on -- of all things -- the subject of aid to starving Cambodia. Ostensibly at issue is the big-think question of whether policy should be shaped by power politics or humanitarian principles -- by Metternich or the Bible.

Actually the question doesn't truly arise in Southeast Asia. The supposed philosophic debate merely provides cover for another episode in the tedious guerrilla war between the State Department under Cyrus Vance and the National Security Council staff under Zbigniew Brzezinski.

The basic facts are complex but clear. Last year Vietnam, backed by Soviet Russia, attacked the Cambodian regime of Pol Pot, which is supported by China. The Vietnamese captured the capital, Phnon Penh, installed a puppet government under Heng Samrin and drove the Pol Pot forces toward the border with Thailand.

But despite massive Soviet aid, the Vietnamese victory was abortive. China intervened on behalf of Pol Pot and occupied part of Vietnam of a brief period last spring. Pol Pot's regime, brutal in the extreme, instituted a scorched earth policy that denied parts of Cambodia to the Vietnamese.

Now the Vietnamese are on the offensive again. The combination of war and scorched earth has yielded mass starvation, particularly evident in swelling refugee camps along the Thai border.

The State Department has favored a policy of unconditional food aid sent to the starving victims from all countries and delivered both by land from Thailand and by ship through Phnom Penh. That approach is grounded in the humanitarian belief that a world flush with food cannot legitimately sit on its hands while millions starve.

In addition, there is the calculation that, in the absence of any aid, Pol Pot's forces would spill into Thailand, bringing the Vietnamese in train. The Thais would feel constrained to respond and call on their American ally for support. With China already pushing Washington to do more for Pol Pot, this country would be dragged into a quarrel among communist powers.

The State Department approach was backed by the president's wife, Rosalynn Carter, who felw to inspect refugee camps when it looked as though Sen. Kennedy might turn the issue against the president. But the department's position has been sharply criticized by the staff of the National Security Council. The NSC staff rightly points out that food sent through Phnon Penh benefits the Vietnamese and their Soviet backers. The NSC has favored a policy that directs food to Pol Pot while fingering the Soviet Union for failure to participate in famine relief.

When the view of the State Department, backed by Mrs. Carter, prevailed, leaks reflecting the NSC position began to appear in the press. Without much doubt, the leaks were planted to discredit State and promote Brzezinski's claim to succeed Cyrus Vance as secretary in a second Carter administration.

Normally this column is to be found in the corner of power politics. My sense is that foreign policy should be governed by national interests, with humanitarian impulses a secondary consideration. I think the Carter administration, and particularly the State Department under Vance, has been blind to Soviet power plays -- especially in Cuba and the Horn of Africa. In my view, the humanitarian impluse to undo the shah fostered in Iran a government clearly detrimental to American security interests.

But in the case of Southeast Asia that logic simply does not apply. This country has no vital interest in the area, and nothing that happens there matters in an important way to the United States. Massive food aid not only answers the humanitarian impulse; it also works to prevent a widening war.

The Bible and Metternich, in other words, yield the same councel, and the supposed clash of philosophic principles is bogus. That is often true, and the lesson is that the hard problem of striking the right balance between interest and principle does not respond to a doctrinaire solution.

Nor should the United States follow a doctrinaire policy. This country ought not to engage the Soviet Union in a full-court press all over the world. On the contrary, the American interest is to stand firm in areas that are strategically important and where this country has a preponderance of weight. What is involved is not brutal power all across the board, but the measured application of the right doses in the right places. So if Brzezinski wants to earn a shot at being secretary, he needs to show not merely the capacity to generalize, but also the capacity to particularize.