In a new indication of U.S. military preparations for possible war against Iraq, the Pentagon is considering basing a small number of B-2 stealth bombers on the island of Diego Garcia in the northern Indian Ocean, officials said Tuesday.

It would be the first time the Air Force bombers have been based outside the United States. They flew many roundtrip attack missions over Afghanistan from their home base in Missouri.

Basing the bombers at the Indian Ocean site would cut in half the distance they would fly to reach Iraq. Because of the special maintenance required to preserve the B-2's radar-evading stealth qualities, climate-controlled shelters would have to be erected on Diego Garcia before the planes arrived.

Several officials, speaking on condition of anonymity, said they were not certain whether the Bush administration had yet asked Britain, which controls Diego Garcia, for permission to erect the B-2 shelters. The New York Times reported in its Tuesday editions that the Pentagon wants to base four to six B-2s there.

Air Force B-1 and B-52 bombers have been allowed to use the island base to launch strikes in Afghanistan; B-52 bombers used the island during the 1991 Gulf War.

In London, a spokesman for the Foreign Office said, "The issue of possible upgrades to facilities on Diego Garcia was discussed at annual talks between the U.K. and U.S. governments. The details of these talks are confidential."

In another development, the Navy is trying to contract for a commercial ship to move military vehicles and other equipment from northern Europe to the Persian Gulf, Trish Larson of the Navy's Military Sealift Command said Tuesday. It would be one of several such contracts arranged recently amid growing signs of an early U.S. military buildup in the Gulf.

U.S. and British fighter pilots, meanwhile, are chipping away at the underpinnings of one of Saddam Hussein's prized military assets: his air defense network.

Defense Secretary Donald H. Rumsfeld disclosed Monday that more than a month ago he ordered that pilots attack command and communications links in Iraq's air defense network rather than the guns and radars frequently used to target or shoot at U.S. and British pilots.

"The idea that our planes go out and get shot at with impunity bothers me. And I don't like it," Rumsfeld told reporters.

The goal of the new approach, more than a decade after American and British pilots began enforcing "no-fly" zones over northern and southern Iraq, is to reduce dangers to the fliers while increasing the damage inflicted on an Iraqi air defense system that has grown more sophisticated.

U.S. officials rarely discuss specifics of tactics used in patrolling the flight-interdiction zones, which Iraq claims are illegitimate violations of its sovereignty. These patrols rarely draw much attention in the United States, but they provide important experience for allied pilots and information about Iraqi activities for U.S. officers preparing plans for a possible war against Iraq.

Destroying or neutralizing Iraq's air defenses probably would mark the opening stage of a U.S.-led invasion.

Rumsfeld's appearance in the Pentagon briefing room marked a subtle but clear change of approach, at least rhetorically. Whereas he previously resisted talking about the possibility of war against Iraq -- he once complained of a news media frenzy -- on Monday he raised the matter himself.

Rumsfeld said the United States cannot afford to put off dealing with Iraq until it has proof Saddam has a nuclear weapon or intends to strike at U.S. interests.

"There isn't a single smoking gun that everyone nods and says, `Aha, that's it,"' Rumsfeld said. "If we wait for a smoking gun in this instance, it obviously would be after the fact. ... You'd find it after lethal weapons were used against the United States, our friends and allies. And that's a little late."

Rumsfeld also made clear he wanted to deliver a message to those in Iraq who might be called upon by Saddam, the president, to carry out an order to use weapons of mass destruction against U.S. or allied forces.

He said these Iraqis, whom he described as hostages to Saddam and "frightened to death" of their leader, should be "very, very careful about their roles in the use of weapons of mass destruction" on Saddam's behalf. Doing so, he said, they would be "nominating themselves as part of the regime." The suggestion in his comment was that they might be spared if they were to defy Saddam's orders.

This week, Rumsfeld is scheduled to testify in the Senate on the Iraqi threat. Next week he will travel to Europe for a NATO meeting at which the allies are to receive an intelligence briefing on Iraq.