The presidential palace in Tikrit was seized without a fight, the military said, and large numbers of U.S. troops were seen in central Tikrit in the afternoon.
"There was less resistance than we anticipated," said Brig. Gen. Vincent Brooks, U.S. Central Command spokesman, noting that Tikrit's defenders had been subjected to punishing airstrikes over the past several days.
In a sign of the easing air campaign, two Navy aircraft carriers will leave the war zone this week, a U.S. official said. The USS Kitty Hawk will return to its base at Yokosuka, Japan, and the USS Constellation will return to San Diego, the official said.
In other developments:
Brig. Gen. John Kelly, the Tikrit operation's commander, said many local people had come forward to point out members of the Fedayeen militia and Saddam's Baath party. Coalition officials initially believed as many as 2,500 fighters had gathered to defend the town.
"This is the heartland of the beast," Kelly said. "The beast is Saddam Hussein. If you were a committed regime murder guy, I guess you'd come here."
Unlike in other major Iraqi cities, however, the many portraits, banners and statues of Saddam remained undamaged.
"We're not going to touch his picture. He's our leader," said Abdul Rahouf Khaled, a construction leader trying to get out of town. Khaled said he wanted the country's next leader to be "someone who is Iraqi and elected by Iraqis."
Monday's combat came after a night of heavy bombing and after Marines made several forays in and out of the city Sunday, drawing occasional small-arms fire and rocket-propelled grenades.
Elsewhere, U.S. forces were working with local authorities in Iraq's cities to restore order after several days of lawlessness, along with power, water service and medical care, Brooks said. Government buildings, hospitals and schools have been damaged or gutted by looters in several cities.
Traffic police were recalled to patrol neighborhoods alongside British troops in the southern port of Basra, and joint patrols were in the works for Baghdad, Karbala and other cities.
With U.S. troops guarding banks and hospitals, parts of Baghdad finally began to return to normal Monday. Shops reopened, traffic snarled and people who had fled the fighting began streaming home.
However, smoke from the Ministry of Trade, the Rashid Theater of Fine Arts, and offices and apartment buildings was a vivid testament that looting and arson continued, and a 45-minute gunbattle outside the Palestine Hotel on Sunday was proof that Baghdad remains a dangerous place.
Sporadic resistance continued in parts of Baghdad. The fighters, often Syrians and other foreigners, were operating individually or in small clusters, said Navy Capt. Frank Thorp, a U.S. Central Command spokesman.
Marines fanning through Baghdad's neighborhoods have found large caches of weapons and ammunition, including about 80 Frog-7 missiles capable of carrying nuclear or chemical warheads discovered in large yellow trucks Monday, Capt. Daniel Schmitt said.
Underscoring the difficulties that could face Iraq's interim administration, a mob in Najaf had for a time surrounded the home of Iraq's top Shiite Muslim cleric and demanded he and other religious leaders leave the country — the latest instance of bitter rivalries erupting in the holy city some 100 miles south of Baghdad.
In the northern oil center of Kirkuk, Human Rights Watch is investigating claims that a group of Kurdish men shot and killed an Iraqi Turkoman boy.
Mosul, Iraq's third-largest city, was calm, with U.S. troops controlling the airport and guarding bridges as well as key intersections. In the old city center, civilians manned checkpoints armed with guns, clubs and metal pipes.
Marines were also working to secure the town of Samarra, about 30 miles to the south, where the seven American POWs were rescued Sunday.