WASHINGTON — Gaza is now run not by a conventional political party but by a movement that is revolutionary, Islamist and terrorist. Worse, Hamas is a client of Iran. Gaza now constitutes the farthest reach of the archipelago of Iranian proxies: Hamas in Palestine, Hezbollah in Lebanon, the Mahdi Army (among others) in Iraq, and the Alawite regime of Syria.

This Islamist mini-replica of Comintern is at war not just with Israel but with the moderate Arab states, who finally woke up to this threat last summer when they denounced Hezbollah for provoking the Lebanon war with Israel. The fall of Gaza is particularly terrifying to Egypt because Hamas is so closely affiliated with the Muslim Brotherhood, the chief Islamist threat to the secular-nationalist regime that has ruled Egypt since the revolution of 1952. Which is why Egypt has just invited Israeli, Jordanian and moderate Palestinian leaders to a summit next week — pointedly excluding and isolating Hamas.

The splitting of Palestine into two entities is nonetheless clarifying. Since Hamas won the parliamentary elections of January 2006, we've had to deal with the fiction of a supposedly unified Palestine ruled by an avowedly "unity" government of Fatah and Hamas. Now the muddle has undergone political hydrolysis, separating out the relatively pure elements: a Hamas-ruled Gaza and Fatah-ruled (for now) West Bank.

The policy implications are obvious. There is nothing to do with the self-proclaimed radical Islamist entity that is Gaza but to isolate it. No recognition, no aid (except humanitarian necessities through the U.N.), no diplomatic commerce.

Israel now has the opportunity to establish deterrence against unremitting rocket attacks from Gaza into Israeli villages. Israel failed to do that after it evacuated Gaza in 2005, permitting the development of an unprecedented parasitism by willingly supplying food, water, electricity and gasoline to a territory that was actively waging hostilities against it.

With Hamas now clearly in charge, Israel should declare that it will tolerate no more rocket fire — that the next Qassam will be answered with a cutoff of gasoline shipments. This should bring road traffic in Gaza to a halt within days and make it increasingly difficult to ferry around missiles and launchers.

If that fails to concentrate the mind, the next step should be to cut off electricity. When the world wails, Israel should ask, what other country on earth is expected to supply the very means for a declared enemy to attack it?

Regarding the West Bank, policy should be equally clear. Palestinian Authority President Mahmoud Abbas represents moderation and should be helped as he tries to demonstrate both authority and success in running his part of Palestine.