THE WAR in the Persian Gulf, now in its sixth year, goes grinding relentlessly on. After a long period of apparent stalemate, the Iranians succeeded several weeks ago in crossing the Shatt al Arab, the river that was the border between the two countries, and taking the Iraqi port city of Faw. The victory does not have great significance in technical military terms. To reach the roads and cities that are more important objectives, the Iranians would have to traverse a broad band of swamp and then open desert in which Iraq's air power and armor presumably would be more effective. But the capture of Faw strengthens the Iranians' sense that time is on their side. Now they have opened another attack in the mountains far to the north. The Iranians are on the move.

Athough the Iraqis started it, after their inital push they have consistently been on the defensive. They have had plenty of time to reflect on the implications of the population balance, in which the Iranians outnumber them three to one. There have been several anxious attempts by intermediaries to negotiate a peace, but all of them have foundered on the same rock -- the implacable hostility of Ayatollah Khomeini. Having entangled itself in a war that seems both unwinnable and unstoppable, Iraq is in an unpleasant position despite the military strength of its defenses. The loss of Faw cannot have done much for the state of mind in Baghdad.

One peculiarity of this long war is the slight attention that it receives throughout the rest of the world. There have been huge battles and horrifying loss of life. Some of the fighting has recalled the trench warfare of World War I. But neither side has allowed outsiders to get close to it -- least of all the kind of outsider who carries a camera. There are few reliable sources other than intelligence satellites.

But if information is meager, the stakes are clear. It's not a local affair. OPEC may be in disarray, but the price of oil worldwide still depends crucially on exports from the Persian Gulf. Throughout the region, political structures are fragile, and one side of this war intends to carry its religious revolution westward into the Arab states. A sudden breakthrough by either side would set off reverberations reaching far beyond the belligerents. A breakthrough still seems less than probable. But, unfortunately, you can't say with confidence that it's impossible.