Updated

U.S. pilots patrolling the skies over Iraq are taking a new approach to defending themselves, and the switch may be chipping away at Iraq's ability to resist a full-scale U.S.-led invasion.

Defense Secretary Donald H. Rumsfeld disclosed Monday that more than a month ago he ordered that pilots attack command and communications links in Iraqi's air defense network rather than the guns and radars that are 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 they can inflict on an Iraqi air defense system that has grown more sophisticated.

U.S. officials rarely discuss specifics of tactics used in patrolling the "no-fly" zones, which Iraq claims are illegitimate violations of its sovereignty. These patrols rarely get much public attention in the United States, but they provide important experience for allied pilots and information about Iraqi activities for U.S. officers who are preparing plans for a possible war against Iraq.

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

Rumsfeld said Bush has not made a decision to go to war.

In Iowa on Monday, the president pressed his case for deposing Iraqi leader Saddam Hussein. Outside the Mississippi Valley Fairgrounds he called him a "tyrant [who] must be dealt with." About 100 demonstrators held signs that read, "Drop Bush Not Bombs" and "Please No War in Iraq."

Bush issued a fresh challenge to the United Nations to show resolve against the Iraqi leader, whom Bush attempted to link -- if only in rhetoric -- to the Al Qaeda terrorists behind last year's Sept. 11 attacks.

The war on terror is more than hunting down Al Qaeda, Bush said. "It also means dealing with true and real threats that we can foresee. One of the most dangerous threats America faces is a terrorist network teaming up with some of the world's worst leaders who develop the world's worst weapons.

"If Iraq's regime continues to defy us and the world, [the United States] will move deliberately yet decisively to hold Iraq to account" with or without the U.N., Bush said.

At the United Nations, Secretary-General Kofi Annan announced that Iraq had agreed to allow, without conditons, the return of U.N. inspectors assigned to seek out and destroy weapons of mass destruction.

In his remarks at the Pentagon, Rumsfeld said the United States cannot afford to put off dealing with Iraq until it has proof that he possesses 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,"' he 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."

In New York, Secretary of State Colin Powell said he was certain the United States will move ahead on a new Security Council resolution ensuring a tough U.N. stand against Iraq to force the country to accept weapons inspections.

The Bush administration is still working to win congressional support.

In a letter to Bush released Monday, Rep. Ike Skelton, the senior Democrat on the House Armed Services Committee, raised numerous questions about the wisdom of launching a military operation.

"The case has not yet been fully made as to what the threat is, why military force is an appropriate way of addressing the threat, and why action must occur now," Skelton wrote. While stressing that he does not oppose the military option, he urged Bush not to "take the first step without considering the last."

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.

In his remarks at the Pentagon on Monday, Rumsfeld said that late last year it was decided that U.S. and British pilots who fly almost daily over Iraq should change their flight patterns to avoid certain areas, Rumsfeld said.

Although U.S. and British pilots do not always fire back when Iraq fires surface-to-air missiles or anti-aircraft artillery at them, the approach in years past was to respond by dropping bombs on the Iraqi missile launchers, anti-aircraft artillery emplacements or the radars used to cue them. Rumsfeld said that after he took office in 2001 he saw growing dangers and diminishing gains.

"It really did not make an awful lot of sense to be flying patterns that we were getting shot at if, in response, we were not doing any real damage that would make it worth putting pilots at risk," he said. The U.S. and British retaliatory strikes were "only marginally effective," he added.

Some months later Rumsfeld ordered that pilots switch their target priorities.

"Instead of going at the specific radar that was involved, which can easily be moved between the time a missile is fired and the time we're able to counterstrike, they're picking on targets that are still part of that continuum of air defense but that are not conveniently moved and can be struck readily," Marine Corps Gen. Peter Pace said in a joint appearance with Rumsfeld at the Pentagon.

This includes such things as communications sites, command centers and fiber-optic links.

Pace said recent strikes have "degraded the air defense capabilities" of Iraq, but Rumsfeld was less sanguine. Rumsfeld said the strikes have damaged Iraq's air defenses but it is not possible to say for sure whether they are being weakened faster than Iraq can rebuild and improve them.