The report comes amidst street by street fighting in the town of Hindiya, where U.S. Army troops Monday pushed their way into the town by battling Iraqi forces over a bridge across the historic Euphrates River.
The prisoners told the Americans they belonged to the guard's Nebuchadnezzar Brigade, based in Saddam's home area of Tikrit, and they had the guard's triangular insignia.
The dawn assault on the key river crossing is the closest known point in the U.S.-led advance on Baghdad, where a battle with the Republican Guard, the best-trained Iraqi troops, looms.
Further south, the Army encircled the Shiite holy city of Najaf and said it killed about 100 paramilitary fighters and captured about 50 Iraqis.
At least 15 Iraqi troops were killed in the fighting in Hindiyah, located 50 miles south of Baghdad between the sacred city of Karbala and the ruins of ancient Babylon. The 4th Batallion of the 64th armored regiment rolled in to the town of 80,000 at dawn — met quickly by small arms fire and rocket propelled grenades from Iraqis hiding behind hedges and brick walls.
Word of the captures in Hindiyah followed a high-level Pentagon assessment that some of the Republican Guard units surrounding Baghdad have been hit so hard by airstrikes they are at less than half strength.
General Richard Myers, chairman of the Joint Chiefs of Staff, says he imagines the morale of the Republican Guard "is a little low right now because they've lost a lot of their force... Their fighting capability is going down minute by minute, hour by hour. There's not going to be much left to fight with."
In Baghdad, coalition forces are continuing bombing raids, focusing on Iraqi leadership targets, command and control centers and communications facilities. A fire was burning at the Information Ministry after the overnight raids, yards away from a shopping mall named for Saddam Hussein.
Iraqis have tried to prevent the U.S. airstrikes over the capital by setting smoky fires, but the U.S. bombing was as intense as ever.
The aerial assault came as U.S. troops were reported to be getting ready to move against Republican Guard forces protecting Baghdad.
CBS News Correspondent David Martin reports the 3rd Infantry Division has begun sending out armed reconnaissance patrols, probing the Republican Guard lines in preparation for the start of an offensive against the elite Iraqi forces.
More and more of the missions flown by the Navy and Air Force are now being aimed at the Republican Guards. In the last 24 hours, warplanes dropped 1,200 precision-guided weapons, the most "smart bombs" dropped in a single day and a sure sign that the air war, which now includes carpet-bombing by B-52s, is focused on enemy troop positions.
Separately, top Pentagon and administration officials defended their war strategy against new criticism that they underestimated the enemy and started the war with too few troops.
In other major developments:
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.
British troops moved into villages on the fringes of Basra, the southern city where an outnumbered but tough core of Saddam loyalists have held off the coalition for about a week.
Up to 1,000 Royal Marines and supporting troops, backed by heavy artillery and tanks, staged a commando assault in a Basra suburb, killing some 30 Iraqi fighters and destroying a bunker and several tanks. Officials said Operation James named for James Bond was the Marines' largest mission so far.
Defense Secretary Donald H. Rumsfeld denied published reports Sunday that he had rejected requests from U.S. war planners for additional troops.
Rumsfeld said the plan developed by Gen. Tommy Franks, is "a good one and it's working. I think the people who are talking about it really are people who haven't seen it."
At the war front, Gen. Franks, the commander of U.S. forces in Iraq, said the campaign was on track.
"We're in fact on plan. And where we stand today is not, in my view, only acceptable, but truly remarkable," he said at the U.S. Central Command headquarters in Qatar.
In Nasiriyah, where fighting has been fierce for a week, Marines secured buildings held by an Iraqi infantry division that contained large caches of weapons and chemical decontamination equipment.
The Army's 101st Airborne Division surrounded Najaf, a key city 100 miles south of Baghdad, on Sunday and was in position to begin rooting out the paramilitary forces inside the city, said Command Sgt. Maj. Marvin Hill.
Following a suicide attack that killed four American infantrymen near Najaf on Saturday, U.S. soldiers say they will now take extra steps to make sure this doesn't happen again, including putting out a road sign that says, "Stop here or you will be killed."
CBS News Correspondent Jim Axelrod, traveling with the 3rd Infantry in central Iraq, says that since Saturday's attack, two other drivers have been shot and killed at the scene of the bombing for ignoring orders to stop and turn around. And drivers of three other taxicabs were shot trying to run three other roadblocks.