In an intensified effort to divide Iraqi President Saddam Hussein from his inner circle, U.S. military and intelligence officers in recent days have communicated with some Iraqi commanders and have secretly designated buildings in the capital for defectors to occupy, promising they will not be targeted by U.S. airstrikes, senior U.S. officials said yesterday.

U.S. military and intelligence officers have also gained promises from some Iraqi commanders that they will not fire chemical weapons at American ground forces, the officials said. However, U.S. officials said they are monitoring one Republican Guard unit outside Baghdad that they believe has been issued artillery shells filled with chemical agents.

As U.S. warplanes made a thunderous show of force in Baghdad and other cities and as American ground units pushed north toward the capital, an invisible but equally purposeful campaign was underway to divide the Iraqi leadership and eliminate the government's inner circle. A major part of that effort, officials said, was communicating with potential defectors -- both in the government and the military.

"There are lots of people, all trying to give the Iraqi commanders options and ways to end the resistance," one senior U.S. official said.

U.S. officials said they still don't know the results of the Thursday bombing of a compound in southern Baghdad where U.S. intelligence believed Hussein and his two sons were spending the night. But they said there are signs that the government and its senior leadership are under unprecedented internal pressure, even if those in the bunker survived the attack by Tomahawk cruise missiles and two 2,000-pound bunker-busting bombs.

Intelligence analysts said that, short of absolute proof, they were operating under the assumption that Hussein and his sons, Uday and Qusay, were still alive, though some officials said there was growing belief that the Iraqi president was injured and had gone into hiding.

"There is not much evidence of central control," a senior administration official said, adding that this may be a sign that both Hussein and his younger son, Qusay, who commands the Republican Guards charged with defending Baghdad, are out of circulation, at least temporarily. Uday, who years ago was wounded in an assassination attempt, runs Iraqi media properties.

The campaign to encourage defections within the Iraqi leadership includes activating phone trees between Iraqi commanders and relatives living outside those parts of Iraq controlled by the Hussein government who are being used as conduits for U.S. information, government sources said. It also includes Internet and shortwave radio communications and hand-delivered messages being brought into Baghdad by individuals who frequently visit the capital.

Asked how the Iraqi inner circle would surrender if it wanted to, Defense Secretary Donald H. Rumsfeld said only: "They know precisely what to do."

U.S. officials said last night they saw signs that Hussein and his senior ranks were unable to simultaneously maintain control over army commanders, search for traitors who may have tipped off U.S. intelligence about the president's whereabouts, and defend the government against the approaching American military onslaught on the capital.

"The regime is starting to lose control of the country," Rumsfeld told reporters. "Their ability to see what is happening on the battlefield, to communicate with their forces and to control their country is slipping away."

Standing with Rumsfeld at a Pentagon news conference, Air Force Gen. Richard B. Myers, the chairman of the Joint Chiefs of Staff, sent the most public of the many messages U.S. military and intelligence officials were directing to Iraqi commanders.

"To commanders and soldiers in the Iraqi forces," Myers said, "I urge you in the strongest possible terms, do the honorable thing, stop fighting, that you may live to enjoy a free Iraq, where you and your children can grow and prosper."

Officials said the message will be disseminated by Commander Solo psychological warfare aircraft that have been broadcasting U.S. military propaganda across southern Iraq for months using AM, FM and shortwave frequencies. The military has dropped tens of millions of leaflets urging Iraqis to tune in to the broadcasts.

Despite the signs of disarray within the Iraqi leadership, intelligence and military officials played down the possibility of an imminent collapse or even that the United States had succeeded in severing all communications between Iraqi units and their commanders. "They had redundant systems," Rumsfeld said. "Our expectation is that, even if it's simply couriers, they will have the ability to communicate."

With U.S. and British troops possibly only days away from Baghdad, time is running out for a nearly yearlong covert effort by the CIA to topple the Iraqi leadership and avert a final battle for control of the capital. Rumsfeld, explaining the military's approach, told reporters yesterday that because a large number of senior Iraqi military leaders had not "separated themselves from that regime . . . the only choice one has is to proceed and use coercion."

Still, Iraq experts said they believe Hussein, even if he has survived, could face potential assassination from inside his ranks. The Iraqi leader's normal protection devices failed him on Thursday, leading to the surprise U.S. air attack on the residential compound in Baghdad. For someone obsessed with security, the attack could be disorienting at a time when Hussein is also supposed to issue commands to thwart the military attack by U.S. and British forces.

"Saddam is obsessed with his own security and spares no expense, including his own time and attention, to ensure his safety," said Kenneth Pollack, a former CIA analyst who has written a book on Iraq. Hussein has employed separate rings of bodyguards and security service personnel, many of whom are members of his clan and are sworn to protect him.

Pollack said yesterday that the airstrike on the bunker, "even if it did not hurt him, probably did a lot of damage in a psychological sense."

He said the Iraqi leader normally prepares five or six locations where he plans to stay for the evening and then chooses one only at the last minute. For the United States to have found where he was, Pollack said, "meant either that there was a spy in his entourage or a new American technical means of monitoring him."

That realization, Pollack said, probably would cause Hussein or his inner circle to embark on "a bloody goose chase to find out" where the information came from. To avoid having his electronic communications intercepted, Pollack said, Hussein "may stop communicating and then only go with couriers" carrying hand-delivered messages. "He may start killing people around him who are important in running the government, and this might provoke people to move against him," he said.

"He has always believed that coups are going on around him all the time," said one former senior CIA analyst, "but with American forces in Iraq and heading towards him, this is unique."

Pollack said that only Hussein's son Qusay, his personal secretary Abid Hamid Mahmud Tikriti, and cousin Ali Hassan Majid Tikriti -- a onetime defense minister -- could give commands in his name. Although the Iraqi military high command is considered competent, Pollack said, it generally acts only on orders from Hussein or one of the other three.