U.S. troops are ready to launch a major assault against Iraqi Republican Guard forces protecting Baghdad, but the commanding general may wait for pressure to build on Saddam Hussein before striking, war planners said Sunday.

"We have the power to be patient in this, and we're not going to do anything before we're ready," said Gen. Richard Myers, chairman of the Joint Chiefs of Staff. "We'll just continue to draw the noose tighter and tighter."

Myers and Defense Secretary Donald H. Rumsfeld said coalition ground forces were closing in on Baghdad from the south, west and north. The U.S. troops south of Baghdad were within 49 miles of the capital, Rumsfeld said, and reporters traveling with those units said several were on the move again Sunday.

More significantly, Myers said days of relentless airstrikes had reduced some Republican Guard units to less than 50 percent of their prewar capacity. Armed reconnaissance elements of the Army's 3rd Infantry Division also have fought with Republican Guard units, Myers said.

U.S. war planners want to be sure the Republican Guard -- the best trained and equipped of Iraq's military -- are significantly softened up before coalition troops meet them in ground fighting. During the 1991 Gulf War, for example, U.S. ground forces didn't attack until Republican Guard units had lost 50 percent to 60 percent of their capacity.

American commanders have a target percentage in mind for the degradation of the Republican Guard before launching the ground assault, a senior defense official said Sunday, speaking on condition of anonymity. Officials will not discuss the goal to avoid revealing their strategy.

Parts of the Army's 82nd Airborne and other units moved into south-central Iraq over the weekend to help protect supply lines that have come under attack by Iraqi forces. Other U.S. fighting units, including members of the 3rd Infantry Division, moved closer to the Republican Guard forces between them and Baghdad.

The U.S. military has detected signs that reinforcements are being sent to some front-line Republican Guard units, while other Iraqi units are pulling back, closer to Baghdad, the senior official said.

A military official said coalition aircraft focused 60 percent of nearly 800 strike sorites Sunday on three Republican Guard divisions around Baghdad: The Hammurabi, to the north, west and south; the Medina, to the south; and the Baghdad, centered southwest of the capital around Kut.

"I imagine their morale is a little low right now because they've lost a lot of their force," Myers said. "Their fighting capability is going down minute by minute, hour by hour. There's not going to be much left to fight with."

Myers and Rumsfeld, making the rounds of the Sunday television talk shows in Washington, would not say when the ground assault on Baghdad would begin. Both predicted such fighting could be brutal.

"It's going to get more difficult as we move closer to Baghdad," Rumsfeld said. "I would suspect that the most dangerous and difficult days are still ahead of us."

The attack on Baghdad, population 5 million, might not be a siege of the city, Myers said, saying the term "conjures up, sometimes, some really bad images."

"It will not be a sort of siege that people have thought about before," Myers said. "We have plans for several different contingencies."

Pentagon officials continued Sunday to raise the possibility that Iraq could use chemical weapons.

"There is no doubt that they have chemical weapons, that they have weaponized them, they have them in artillery shells," Myers said. "They probably have other means of delivery."

He cited the discovery by coalition forces of protective gear and nerve agent antidotes left behind by Iraqi military and paramilitary forces. Myers said the discoveries indicate that Iraqi troops planned to wear the protective gear while using chemical weapons.

Marines searching a compound used by Iraq's 11th Infantry Division in the Euphrates River city of Nasiriyah on Saturday found more than 300 chemical protection suits and gas masks, U.S. Central Command reported. The Marines also found atropine injectors -- antidotes for nerve agents -- and chemical decontamination vehicles and devices, Central Command said.

Earlier last week in the same city, Marines found more than 3,000 chemical protection suits in a hospital used by Iraqi paramilitary forces as a base.

Also Saturday, British troops south of Basra found Iraqi training equipment for nuclear, biological and chemical warfare -- including a Geiger counter, nerve gas simulators, gas masks and protective suits, according to British press reports.