With all of Iraq's major cities under U.S. or British occupation, a Marine armored column moved north out of Baghdad today in the direction of Tikrit, the ancestral home town of ousted president Saddam Hussein, to join in an effort to squeeze and eventually eliminate the last vestiges of his once-powerful Baath Party government, U.S. officials said.

A U.S. Central Command spokesman said the Marines would "commence ground operations [against] suspected Iraqi military strongholds" north of Baghdad, and officials in Washington made it clear the target was the Tikrit region, about 90 miles north of the capital. The task force commander, Brig. Gen. John Kelly, was quoted as saying he was "moving northward out of Baghdad" and would give a chance to "anyone who wants to surrender" instead of being destroyed.

Twenty-four days into the war, Tikrit has become the last center of any size suspected of harboring Hussein loyalists, although U.S. military officers say the numbers involved and their readiness to fight are uncertain.

[A CNN team reported Sunday morning from inside Tikrit that the town did not appear to be heavily defended but remained in the hands of forces apparently loyal to Hussein. Reporter Brent Sadler and others in a CNN vehicle were fired on by guards at a road checkpoint and by gunmen who pursued them briefly as they fled the city.]

Looting and sporadic shooting plagued Baghdad for the third straight day, meanwhile, and U.S. military patrols failed to quell continued street violence between Arabs and Kurds in Mosul, which was abandoned Friday by its Iraqi defenders.

The highest-ranking Iraqi official to surrender so far, Gen. Amir Saadi, Hussein's science adviser, turned himself in to U.S. soldiers in Baghdad, using a television crew from Germany's ZDF network as intermediaries. Saadi told the television reporters he had no idea whether Hussein was alive or where he might be, and he reiterated that the Hussein government had no chemical or biological weapons -- the main reason cited by the Bush administration in launching the war.

President Bush, in his weekly radio address, cautioned that the war was not yet over and that "hard fighting" could still lie ahead despite the military campaign's overall success. But residents of Iraqi cities, especially Baghdad, complained that U.S. troops were not moving swiftly enough into a peacetime posture, in particular to end a tidal wave of looting that has swept over the country's government buildings, hospitals, warehouses and official residences.

Seeking to ease restrictions on normal activities in Baghdad, U.S. forces reopened two bridges spanning the Tigris River to civilian traffic. But the immediate result was that looters raced across and extended their plundering to the Planning Ministry and other buildings that had been spared. People were seen carting way computers, shelves, sofas and other office furnishings.

The State Department announced it will send two dozen police officers and other law enforcement officials as a down payment for a force of nearly 1,200 to help organize an Iraqi police system to restore order. Getting a jump on the process, police officers in Baghdad met with U.S. military officers in an effort to organize redeployment of normal Iraqi police forces untainted by association with the abuses of Hussein's three-decade rule.

Col. Mohammed Zaki, an Iraqi police officer, told reporters U.S. Marines and Iraqi police will begin joint patrols within a few days in the capital. Marine civil affairs officers agreed that joint patrols would be a good idea, but they did not predict when they could start.

Maj. Frank Simone, one of the civil affairs officers, told the Associated Press that the difficulty lies in distinguishing between police officers who could present a danger to U.S. forces -- by informing on them to die-hard Hussein loyalists -- and others who could be useful in meeting residents' pleas for increased security and a resumption of municipal functions.

"Most of the top people, the ones we think are Baath officials, the ones that fled, are guys that we don't want to come back," he said. "But a lot of the ones that stayed are good guys."

Despite the cries for a return to normality, an Army unit reported a sharp clash with Iraqi irregulars in the western part of Baghdad, in which officers said about 20 Iraqi militiamen were killed and no U.S. soldiers were lost. But a Marine guarding a hospital on the eastern side of the Tigris River was shot and killed when two Syrian men posing as gardeners sneaked up, pulled out a concealed gun and opened fire at point-blank range. Other Marines at the checkpoint returned fire, killing one of the assailants and injuring the other, officers reported.

At another checkpoint, Marines fired at a vehicle that ignored repeated signals to stop, killing one occupant and injuring another, officers here at headquarters said. Because of several suicide bombings, soldiers and Marines have received orders to be extremely vigilant against oncoming Iraqi vehicles.

U.S. military officers said troops in the arid western stretches of Iraq stopped a bus apparently heading for Syria and found 59 men carrying $630,000 and letters promising rewards for those who killed U.S. soldiers. Brig. Gen. Vincent Brooks, briefing reporters at the Central Command's regional headquarters in Doha, Qatar, said the money was in $100 bills but the nationality of the men and the source of the letters were unclear.

Officials voiced suspicion that the 59 were among several thousand non-Iraqi Arabs who volunteered to come to Iraq and help Hussein's forces defend against the U.S.-British invasion. U.S. officers have reported encountering non-Iraqi fighters for the last several days in Baghdad.

U.S. officials in Washington have accused the Syrian government of permitting the Arab volunteers to enter Iraq through Syria and of aiding Hussein's forces by shipping night-vision goggles to them. But Foreign Minister Farouk Charaa disputed those charges today, describing them as "baseless allegations."

Marines said some of their troops searching an elementary school in an affluent neighborhood near the center of Baghdad found more than 150 garments lined with explosives that they believe were designed to be worn by suicide bombers. The vests were scattered on the floor of a classroom, still wrapped in plastic and on hangers, according to Capt. Tom Lacroix, commander of Charlie Company in the 1st Battalion, 7th Marine Regiment.

Marine explosives experts described three types of garments: black leather vests lined with vertical ribs made of explosives, bibs filled with explosives and hundreds of steel balls that would serve as shrapnel when the bib was detonated, and wide belts packed with explosives.

Some of the devices were equipped with a hand-operated trigger mechanism, while others were rigged with mercury that would cause them to be detonated when the wearer raised his or her arms. Each came with an instruction card, printed in Arabic, and were marked "Made especially for Saddam's Fedayeen."

Lacroix said the Marines plan to destroy the garments with explosives.

Marines have uncovered dozens of major weapons caches in recent days as they continue patrols and gather information from Iraqi citizens. This morning, a Baghdad resident led Marines from Charlie Company to a yellow trailer, parked in a residential neighborhood about three miles from the school where the vests were discovered. Inside they found four missiles, roughly 40 feet long. The missiles bore tags written in Russian and looked new, he added.

"Everything we heard about the sick things they would do, like hiding this stuff in places where children are, is coming true," said Lacroix, of Guilford, N.H. "The more we dig, the more we'll find."

The forces headed toward Tikrit, Task Force Tripoli, were to be joined later by elements of the Army's 3rd Infantry Division, also planning to move up from the Baghdad area, Pentagon officials said. The Marines encountered enemy fire along the road about 20 miles north of Baghdad, officers here said. The Marines engaged in a sustained gun battle with the attackers, which ended without reported U.S. casualties.

"It wasn't just shoot and scoot," said Maj. Glindon Ashbrook, ground operations officer at Marine headquarters, referring to the short-lived ambushes characteristic of Iraqi paramilitary squads that harassed U.S. troops in southern Iraq. "These guys were protecting something or someone."

Many military strategists predicted Tikrit would be a fortress filled with Hussein's tribal allies willing to fight to the death, and some U.S. intelligence suggests that may yet be the case. But video of the city shot from a reconnaissance plane has found no major military formations. Instead, it showed signs of abandoned military equipment and looting in the streets.

"We may find that there's not much fight left, but some of the recent operations indicate that there's still some fighting to do even in those areas," said Brooks, deputy director of operations for the U.S. Central Command.

Maj. Barry Montgomery, a Marine intelligence officer, said there may still be some remnants of the Adnan Division of the Republican Guard as well as some paramilitary forces around Tikrit. But the government's command and control appears to be gone.

"There doesn't appear to be someone pulling the strings," he said.

The move toward Tikrit came as the Marines formally secured the strategic city of Kut, about 100 miles southeast of Baghdad.

Intelligence had indicated last week that Iraqis and their Arab guerrilla allies had regrouped in Kut. But local leaders told approaching Marines that Shiite Muslim fighters had already driven out the Hussein loyalists. The local leaders invited the Marines in today and met with Lt. Gen. James T. Conway in a celebratory event that mirrored the reception U.S. troops received in Baghdad Wednesday.

"It was like a Fourth of July parade today," said Gunnery Sgt. Steve Soha, 40, a Marine reservist who normally works as a police officer in Phoenix. "Everybody was out in the street, waving and happy. It was amazing."

Staff writer Jonathan Finer in Baghdad contributed to this report.

A Marine shouts orders as his unit takes positions on the eastern bank of the Tigris River in Baghdad as sporadic firefights continued in the Iraqi capital. An Iraqi family stands in their driveway as a Marine patrols through Baghdad, a city that is still plagued by looting. Fakradeen Rabid Abdulla, a Kurdish man in Kirkuk who has one remaining tooth, says Kurdish militias should stay in the city to maintain order.