THE NEWEST NATION is Belize, a small, mainly black, English-speaking sugar-exporting democracy on Central America's Caribbean shore that was a British colony (you remember British Honduras) for 119 years until just the other day. It comes into independence with a reputation as a relatively well-run place so far little touched by the torments afflicting most of its neighbors, and with a respected and moderate leader, George Price, prime minister since Belize gained self-government in 1964.

But Belize has a pressing problem: Guatemala. The Guatemalans, who are pretty much everything that the people of Belize are not, claim Belize on the basis of a 19th century colonial treaty. British diplomats tried to work out a deal before independence, but the Guatemalans, preferring to wait for the whole loaf, would have none of it. The military dictatorship in Guatemala City has been breathing nationalistic fire ever since. The new ministate has no defense force of its own to speak of.

For the moment things are steady. The British have put 1,600 Gurkhas into Belize "for an appropriate period," and they have helped Prime Minister Price obtain a shield of political assurances from nearby members of the British Commonwealth and other neighbors. The United States has been induced to put in a warning word with the generals it has been talking to, for other reasons, in Guatemala City. In the longer term, however, there can be no suitable substitute for an unequivocal Guatemalan acceptance of the independence that virtually every single one of Belize's 145,000 citizens wants. If the dictator currently sitting in Guatemala City cannot do it, some successor must.