Brig. Gen. Vincent Brooks, at the daily briefing at U.S. Central Command in Qatar, insisted U.S. war planners had not underestimated Iraqi fighting capabilities, but said unexpected developments were inevitable in any war. He accused the Iraqis of using "terrorist death squads" who changed in and out of civilian clothes. 

U.S. and British aircraft are pounding some of the estimated 30,000 Republican Guard forces arrayed around Baghdad and striking inside the capital against Saddam's levers of power and modes of communication. 

The military early Friday rolled out new weapons - two 4,700-pound, satellite-guided "bunker busting" bombs were dropped from American B-2 bombers on a major communications tower on the east bank of the Tigris River in downtown Baghdad. The bombs were twice the size of the bunker busting bombs that were being used before. 

The bombing attack, aimed at disrupting communication between Saddam and his military leaders, gutted a seven-story telephone exchange, leaving the street strewn with rubble. 

Powerful explosions rocked the capital during the night and Friday morning aircraft swooped low over the city. Anti-aircraft fire was intermittent. 

Iraqi Information Minister Mohammed Saeed al Sahaf said the overnight air strikes killed seven people in Baghdad and wounded 92. 

While the coalition war plan is flexible and certain to shift with events, U.S. leaders say they are operating on three rock-solid certainties: They won't lose. They won't set a timetable. And they won't let up until Saddam is gone. 

"There isn't going to be a cease-fire," Defense Secretary Donald H. Rumsfeld told lawmakers on Thursday. 

Rumsfeld also raised the possibility of a siege of Baghdad rather than a quick strike into the heart of the city. 

Asked by Sen. Pete Domenici, R-N.M., what American ground troops would do once they reached Baghdad, Rumsfeld answered by saying Baghdad had to be isolated before it was taken. 

He also alluded to what is happening at Basra, Iraq's second-largest city. British forces there have laid siege, hoping for a successful uprising by the city's Shiite population. 

Rumsfeld noted that both Basra and Baghdad have large numbers of Shiites. "And they are not terribly favorable to the regime. They've been repressed," Rumsfeld said. 

American Army and Marine infantry forces are arrayed to the south of Baghdad, some within 50 miles of the capital. They are led by the Army's 3rd Infantry and 101st Airborne divisions and the 1st Marine Expeditionary Force. 

Coalition special operations forces are working both in western and northern Iraq, and the Army's 173rd Airborne Brigade has secured an airfield in the north with 1,000 paratroopers. And more are on the way. 

The movements suggest a strategy to encircle Baghdad with U.S. troops much as Saddam has ringed the city with his best trained and best equipped Republican Guard forces. 

Special forces have cleared large areas of western Iraq, creating a crucial buffer to ensure Saddam's forces cannot launch missile strikes on neighbors such as Jordan, Saudi Arabia and Israel, a senior U.S. military commander said. 

About 90,000 U.S. troops are inside Iraq, a senior defense official said Thursday, adding that was an increase of about 14,000 in just two days. More than 250,000 U.S. troops are in the region, including thousands aboard Navy ships at sea, on air bases in surrounding countries and at headquarters encampments. 

Another 100,000 to 120,000 ground troops are expected to begin arriving in Kuwait in coming days, including the Army's 4th Infantry, 1st Armored and 1st Cavalry divisions. 

Iraq's defense minister on Thursday confirmed what many U.S. military officials suspected was Saddam's strategy: Draw the coalition ground troops into Baghdad for a long, bloody, street-by-street battle. 

"The enemy must come inside Baghdad, and that will be its grave," Defense Minister Sultan Hashim Ahmed said. "We feel that this war must be prolonged so the enemy pays a high price."