The Saudi monarchy, concerned about a public backlash against the war and fearful of inflaming the passions of Muslim extremists, is going to great lengths to cloak the degree to which it is cooperating with the United States against neighboring Iraq.

The sensitivity about the U.S. troop presence here is so acute that even souvenir snapshots pose a sensitive diplomatic challenge at the remote Saudi desert air base, not marked on any map, where U.S. forces direct the air war against Iraq.

Under Saudi-imposed rules, no photos can depict anything that reveals U.S. forces operating at their high-tech command center at the Prince Sultan air base. No landmarks. No signs. No Saudis walking in the background. No vehicles with Saudi license plates. All snapshots are reviewed, and once a week the base holds a "morale day" in which a photographer takes group shots against a bland backdrop that could be anywhere.

"Take pictures in front of a plain brown wall and you're okay," said Lt. Col. Joseph LaMarca, an Air Force spokesman interviewed by telephone because the Saudis have barred reporters from the base.

Public sentiment is almost universally opposed to the war, and officially, the Saudis are not involved in it. In a carefully parsed address televised this week, Crown Prince Abdullah, de facto Saudi ruler on behalf of ailing King Fahd, vowed: "The kingdom will not in any way participate in the war on Iraq. Its forces will not in any way enter one inch of Iraqi territory."

But diplomats here say the Saudis have granted the U.S. military permission for everything it needs, if not everything it wants, at Prince Sultan and at two other remote airstrips that are closed to the public and reporters. An estimated 5,000 troops are at the air base and their numbers could double, according to diplomats. Even many well-connected Saudis do not realize the extent of their country's cooperation with the United States, but few are deceived by the government's euphemisms, denials and silence.

"When [Defense Secretary Donald H.] Rumsfeld said so many countries are cooperating who do not want it known, everyone assumed he was talking about Saudi Arabia," said Turki Hamad, a political scientist.

Saudis are adept at reading between the lines and deciphering the meaning of seemingly contradictory statements. For example, the princes who rule the country regularly extol the virtues of a policy they characterize as progress without change.

But the presence of the Air Force at Prince Sultan, which has begun to look more permanent as tents have given way to barracks, has been increasingly difficult for the Saudis to ignore.

After the 1991 Persian Gulf War, thousands of U.S. troops stayed in Saudi Arabia to patrol the "no-fly" zone over southern Iraq. That is no secret. The government says the Americans are merely enforcing international agreements.

But some militant Muslims consider it blasphemy for foreign troops to set down stakes in the birthplace of the prophet Muhammad and home to the two holiest shrines in Islam.

The depth of their anger grew apparent with the Sept. 11, 2001, attacks in the United States. Fifteen of the 19 hijackers were Saudis associated with al Qaeda. Osama bin Laden is a native Saudi who cited the presence of U.S. forces here as reason to target the ruling Saud family and the United States. The government recently announced it had arrested 95 al Qaeda sympathizers in the kingdom, a disturbing sign to many Saudis that the militants had more of a foothold than they had believed.

The end of Saddam Hussein's government would mean some U.S. troops could leave, though not all. In private conversations, Saudi officials acknowledge being embarrassed by their ties to Washington when its troops are invading Iraq and when the Palestinians and Israelis are at each other's throats. But diplomats say the Saudis have assured the United States that it wants U.S. troops to maintain a deterrent presence here.

"The Saudis would like to see things return to pre-1990, with the U.S. presence over the horizon and understated," said a diplomat in Riyadh. "It obviously has a destabilizing effect for Saudi Arabia, and for America."

Prince Sultan air base also served as the air command center for the war in Afghanistan. Most U.S. personnel moved there from Dhahran after the Khobar Towers bombing in 1996, and tents have been erected to house the influx of new troops and contractors. From the $45 million Combined Air Operations Center (CAOC), a 120,000-square-foot building completed in mid-2001, the Air Force monitors images from drones, E-3 AWACS reconnaissance planes and satellites to identify targets for bombing runs and to make damage assessments.

"For the first time, we have one commander in charge of all air forces in the region," LaMarca said. "All the air tasking orders and all the planning for the air campaigns comes out of here."

Bowing to Saudi concerns, the United States promised not to launch any offensive operations from Prince Sultan, a sprawling 250-square-mile compound -- the size of metropolitan Chicago -- located on an unmarked road in the desert 70 miles southeast of Riyadh. But the Saudis have been secretive about what does go on at the base and at air strips at the towns of Arar and Tabuk.

Prince Sultan, the Saudi defense minister, has said that Arar is being used to assist Iraqi refugees, who will be kept on the Iraqi side of the border 40 miles away. Foreign "friends," he said, are there only to provide "humanitarian and technical assistance." But diplomats in Riyadh say U.S. troops are using the base for surveillance and for search and rescue missions.

Jamal Khashoggi, a Saudi political analyst and editor of the newspaper Al-Watan, said the Saudi cooperation in the war is an open secret.

"People know the Americans are here," he said. "The war is going on, so they must have a role. There's a clear message of involvement. But what people also know is that Saudi Arabian troops will not be fighting in the war."