Though the United States is the strongest military power in the world, there are sharp limits to how much it can punish terrorism. And to the extent it's hard to punish terrorism, it's hard to deter it.

That much should be clear from this week's cowardly attack in which a powerful truck bomb ripped through a building in Saudi Arabia housing U.S. Air Force personnel, killing 19 Americans and injuring some 300 other people.The death toll made it the worst terrorist blast involving Americans in the Middle East since the 1983 barracks bombing in Beirut, Lebanon what killed 241 American servicemen.

Why can't such episodes be prevented? Because it's hard to identify the perpetrators, let alone apprehend them.

Even if punishment could be swift and sure, it doesn't always deter. Just ask Israel, which has suffered repeated terrorist bombings that have killed and maimed innocent people. Just as repeatedly Israel has responded quickly and violently. But such responses have not stopped the terrorism.

Americans can expect no better. That's no argument for the United States to retreat into isolationism. But the public needs to realize that the extent to which U.S. forces are deployed abroad is the extent to which their - and our - vulnerability is increased.

Keep in mind, too, why American forces have been stationed in Saudi Arabia and why they ought to remain there, at least for the time being.

The United States and Saudi Arabia have been close allies for more than half a century. American forces, leading an international contingent, used Saudi territory as a base for the counterattack in the Persian Gulf War that drove Iraqi invaders out of neighboring Kuwait.

American troops have remained in the kingdom since then to keep an eye on Iraq and act as a deterrent to other Iraqi forays. Their presence angers Muslim militants who oppose any Western presence in Saudi Arabia, home to Islam's holiest shrines.

But U.S. policy cannot be based on the demands of militants without sacrificing important American interests. One of those interests is rooted in the fact that Saudi Arabia, owning a quarter of the world's oil reserves, is the globe's biggest petroleum producer and exporter. A fifth of all U.S. oil imports come from Saudi Arabia; a sudden loss of that source would send the American economy reeling. The Saudis have repeatedly moderated oil price hikes engineered by the OPEC cartel. In various other ways, their international policies have been pro-western and pro-American.

Despite all this, an American military presence would not be required if the Saudis and other peaceful nations in the Persian Gulf had formed their own multi-lateral defense force as promised after the gulf war.

This week's terrorist attack on Americans stationed in Saudi Arabia ought to prompt Washington to breathe new life into this proposal by demanding that the Persian Gulf nations do more to protect themselves.