CHINA'S ATTACK on Vietnam, though not unprovoked, is certainly reprehensible. It could be argued that frequent border conflicts between the two countries, Hanoi's expulsion of 180,000 ethnic Chinese and, in particular, its invasion of Cambodia and overthrow of the China-backed Pol Pot regime have forced China to do something to prove its strength and its commitment to supporting its allies.

However, the preservation of peace is more important than China's national pride. China should have called on the United Nations or some other impartial arbitrator to settle the disputes.

China is not the only nation guilty of violent powerplays. Vietnam's invasion of Cambodia--though perhaps provoked by the Pol Pot regime's border raids in Vietnam--was not a defensive action.

Nor was China motivated primarily by moral considerations. Pol Pot's reported massacre of his potential opponents was probably of less concern to Hanoi than the inconvenience of having a Chinese supported government on its border. The Vietnamese puppet regime is no more motivated by humanitarian concerns that was Pol Pot's government.

So far President Carter has limited himself to exhortations of nonaggression, urging the Chinese to withdraw from Vietnam and Vietnam to withdraw from Cambodia. There is not much else he can do. The U.S., no stranger to amoral powerplays in Vietnam, has little or no leverage left in Southeast Asia.

The Soviet Union's restraint is probably also more a matter of necessity than choice. The Russians do not want a war with their giant neighbor and have traditionally been very cautious in their relations with China.

The continuation of war in Southeast Asia is a disheartening threat to world peace. Apparently the governments of China, Vietnam and Cambodia believe that aggression is necessary to maintain their power and prestige. The losers, as always, are the people of those countries.