U.S. Marine patrols made rapid incursions into Saddam Hussein's hometown Sunday and clashed with its scattered defenders, using air strikes and artillery in a bid to overwhelm any plans for a furious last stand at the Iraqi leader's power base. U.S. forces suspected about 2,500 die-hards of the Republican Guard and the paramilitary Fedayeen - and possibly officials from Saddam's regime - were holed up in Tikrit.

Artillery explosions flashed on the horizon, and jets roared overhead.

Still, U.S. forces did not try to occupy Tikrit right away, Pentagon officials said.

Defense Secretary Donald Rumsfeld said there was "no organized resistance" in Tikrit, though the city was "not permissive yet."

After the day's forays, the Marines left a force inside the town to establish a "foothold" ahead of further assaults the next day, a New York Times correspondent with the Marines reports.

US Forces Reject Tribal Offer to Surrender

The Arab satellite station Al-Jazeera reported that local tribal groups offered to negotiate a "peaceful solution" with U.S. forces and hand over some Baath Party leaders in the town. The tribal groups said the regular army; Republican Guards and Fedayeen Saddam left the city five days ago, according to Al-Jazeera.

Tikrit, 90 miles north of Baghdad, is the last major city with substantial resistance by Iraqi forces. Saddam was born in the area, and many members of his inner circle come from the region.

After the fall of Baghdad last week, U.S. commanders cautioned that Saddam's regime might try to hold on ferociously to Tikrit. But they played down that possibility in recent days because of desertions and damage from sustained air strikes.

7 US POWs Rescued

As they moved from Baghdad to Tikrit, the Marines rescued seven American troops held by the Iraqis for three weeks. Iraqi soldiers who had been abandoned by their officers approached the Marines and handed over the POWs.

Gen. Tommy Franks, the war commander, said some Marine units entered Tikrit after a swift advance from Baghdad, but he would not say how far the Marines had gotten.

Before the Marines' arrival in Tikrit, live footage aired by CNN showed no signs of active Iraqi defenses, suggesting that intensive U.S. air strikes had achieved their intended effect.

However, CNN vehicles came under small-arms fire as they tried to enter the city center Sunday. A security guard with the CNN crew returned fire at least twice, and the news crew quickly drove away.

There were no reports of looting or evidence of it in Tikrit.

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US forces have ignored efforts by tribal authorities to negotiate a peaceful end to the siege of Saddam Hussein's hometown.