The TIMING of the ambush of a busload of unarmed American sailors in Puerto Rico suggests a link with the tumult in the Middle East, but in fact there is no connection. What happened in the Caribbean was no more than an act of isolated thuggery. Those who claim to have perpetrated it say they had a broad political purpose, Puerto Rican nationalism, as well as a narrow one: to avenge the recent prison death -- by suicide, officials say -- of a Puerto Rican who had been convicted of trespassing at a protest site. But their act remains one of craven terrorism. They must be condemned. Cuba and the other Third Worlders accustomed to taking cheap shots at the United States in the name of Puerto Rican "independence" deserve their share of the blame for egging them on.

These days some Americans may feel shell-shocked enough to believe that if people are killing Americans, they must have some point or purpose in doing it. But there is no reason here, only rage. The United States is not repressing anything in Puerto Rico. Nationalists there have for years had full legal opportunity to propagate their cause. But although almost all Puerto Ricans have one or another complaint with the current commonwealth status, almost none of them believes nationhood is the way out. The four nationalists whom President Carter recently released from long prison sentences have been muttering bitterly since their return to Puerto Rico that no one pays attention to them. In the circumstances, there is reason to suspect that the flyspeck groups of desperadoes who attacked the Navy bus did so out of intense frustration.

Puerto Ricans note with irritation that they don't make the "continent's" front pages until someone throws a bomb. They have a point. Puerto Rican affairs do merit attention these days because the island is in the throes of reviewing what it wants its relationship with the United States to be. Independence is a loser but statehood is a live contender, and so is an improved version of commonwealth status that would give the island a fuller measure of self-government. Presidents of both parties have said they will honor Puerto Rico's choice. That puts on the island the burden -- a heavy one -- of initiating a change.

Whateverd the choice turns out to be, it will not be self-fulfilling, and the 50 states will have to apply themselves to make it real. It is that sort of serious political attention, not merely a wave at presidential-primary time, and certainly not just a nod at the occasional act of terrorism, that Americans owe their fellow citizens who live in Puerto Rico.