Some of Iraq's Republican Guard units surrounding Baghdad have been hit so hard by airstrikes they are at less than half strength, the Pentagon's top general says.

"I imagine their morale is a little low right now because they've lost a lot of their force," Gen. Richard Myers, chairman of the Joint Chiefs of Staff, said Sunday.

"Their fighting capability is going down minute by minute, hour by hour. There's not going to be much left to fight with."

In street-by-street fighting Monday, U.S. troops moved into the town of Hindiyah, capturing several dozen Iraqis who identified themselves as members of the Republican Guard and killing at least 15 others. The fighting, about 50 miles south of Baghdad, was the closest known battle in the march toward the capital.

Pentagon officials said U.S. troops are prepared for a major attack against Saddam Hussein's elite forces, but the heaviest attack may wait for pressure to build on the Iraqi leader before striking.

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

Nevertheless, Myers and Defense Secretary Donald H. Rumsfeld, making the rounds of the Sunday television talk shows in Washington, predicted an assault on Baghdad 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."

Rumsfeld and Myers 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. 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.

A military official said coalition aircraft focused 60 percent of nearly 800 strike sorties 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.

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, according to a senior defense official, speaking on condition of anonymity.

Defense officials said 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, 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 elite Iraqi divisions before launching the ground assault, said the senior defense official, declining to elaborate.

The attack on Baghdad, population 5 million, will not be a siege of the city, Myers said, adding that "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."

Officials cited the discovery by various coalition forces of chemical protection suits and gas masks; atropine injectors containing antidotes for nerve agents; chemical decontamination vehicles and devices; nuclear, biological and chemical warfare training equipment including a Geiger counter, nerve gas simulators, gas masks and protective suits.