The significant combat phase of Operation Iraqi Freedom is essentially over, Pentagon officials said Monday, and what's left are sporadic pockets of Saddam loyalists who are unlikely to put up a fierce fight.

Saddam Hussein's hometown of Tikrit fell Monday with unexpectedly light resistance, the last Iraqi city to succumb to overpowering coalition ground and air forces.

As fighting wound down, Pentagon officials disclosed plans to pull two aircraft carriers from the Persian Gulf. At the same time, Iraqi power brokers looked ahead to discussions on a postwar government at a U.S.-arranged meeting set for Tuesday.

• Maps: Iraq | Baghdad

"I would anticipate that the major combat engagements are over," Maj. Gen. Stanley McChrystal told reporters at the Pentagon. Tikrit fell with no sign of the ferocious last stand by Saddam loyalists that some military planners had feared.

Secretary of State Colin Powell hinted at economic or diplomatic sanctions against Syria, saying the government is developing a weapons of mass destruction program and helping Iraqis flee the dying regime. Syrian officials denied the charges.

Looting eased in Baghdad after days of plundering at government buildings, hospitals and an antiquities museum, and group of religious and civil opposition leaders met in the capital to plan efforts at renewing power, water, security and other vital services.

American forces found prodigious amounts of Iraqi weaponry, French-made missiles and Russian anti-tank rocket launchers among them. And Army troops discovered thousands of microfilm cartridges and hundreds of paper files inside a Baath Party enclave as the dead regime began yielding its secrets.

In Tikrit, about 90 miles north of Baghdad, "There was less resistance than we anticipated," Brig. Gen. Vincent Brooks told reporters, as American ground troops moved into the city after days of punishing airstrikes.

A senior defense official told Fox News that Baath Party members and members of the Fedayeen Saddam had formed 100 small death squads in Tikrit. Several tribal leaders tried to negotiate a cease-fire with coalition forces but Baath officials resisted their efforts.

American forces captured a key Tigris River bridge in the heart of town and seized the presidential palace without a fight as they rolled past abandoned Iraqi military equipment.

They set up checkpoints to keep prominent regime figures from leaving, and a line of armored vehicles was parked in front of a bazaar inside the city.

"We have had engagements, and we have defeated the enemy in every one of those engagements," said Capt. Frank Thorp, a spokesman at U.S. Central Command.

The operation inside Tikrit, Brooks added, "is really the only significant combat action that occurred within the last 24 hours." McChrystal told reporters, "I think we will move into a phase where it [combat] is smaller, albeit sharp fights."

With Saddam and his two sons dead or in hiding, his regime gone and his armed forces routed, U.S. commanders took steps to reduce American firepower in the war zone.

A U.S. defense official said two of five aircraft carrier battlegroups in the region would soon be leaving, the USS Kitty Hawk returning to its base in Japan and the USS Constellation to San Diego. Each carrier has about 80 warplanes, including F/A-18 and F-14 strike aircraft as well as surveillance and other support craft.

The Air Force already has sent four B-2 stealth bombers home.

In a reminder of lingering hazards, two soldiers with the Army's V Corps were killed and two wounded when a grenade exploded accidentally at a checkpoint south of Baghdad and a third soldier was killed and another wounded in an accidental shooting near Baghdad International Airport, Central Command said.

With fighting on the wane, troops continued their search for remaining POWs as well as evidence of weapons of mass destruction.

Maj. Trey Cate, a spokesman for the 101st Airborne Division, said tests were planned on 11 shipping containers found buried near Karbala with lab equipment inside.

A team of experts from the CIA and Defense Intelligence Agency also has arrived in the Persian Gulf region to search for clues to the whereabouts of Capt. Scott Speicher, a Navy pilot shot down during the 1991 Gulf War, officials said.

U.S. official said an Iraqi nuclear scientist, Jaffar al-Jaffer, had surrendered to authorities in an unidentified Middle Eastern country in recent days and was being interviewed by Americans.

On Saturday, Saddam's top science adviser, Lt. Gen. Amer al-Saadi surrendered to U.S. forces.

In Washington, Powell became the latest senior administration official to accuse Syria of harboring former members of Iraq's regime and of maintaining a chemical weapons program.

"Of course, we will examine possible measures of a diplomatic, economic or other nature as we move forward," Powell told reporters.

Fayssal Mekdad, Syria's deputy ambassador to the United Nations, denied the U.S. allegations. "There is no cooperation. We have no chemical weapons," he said.

In London, British Prime Minister Tony Blair said Syrian President Basher Assad had personally assured him that his government "would interdict anybody" crossing the border from Iraq. "And I believe they are doing that," Blair told the House of Commons.

More and more, efforts were turning to building a postwar Iraq. Officials made preparations for a meeting Tuesday in the southern city of Ur, said to be the birthplace of the biblical patriarch Abraham.

There, Iraqis from inside and outside the country will begin discussions on the shape of a future government.

At the Pentagon, Defense Secretary Donald H. Rumsfeld said "it's not possible to know how long" a process of stabilization will take inside Iraq.

Government offices and most stores remained closed in the capital, but many buses were running, packed with passengers. The first joint patrols moved through Baghdad during the day, with Marines and Iraqis working together.

Police Lt. Col. Haitham al-Ani said American troops and Iraqis would patrol in separate cars and that the Iraqis would be unarmed, at least for now.

At the same time, local leaders met in Baghdad to discuss security and plans to restore water and electricity to a city that has been without power for more than a week. One Shiite Muslim cleric, Ayad al-Musawi, told the meeting there should be "no Sunni, no Shiite, just one Iraqi nation."

He added, "God willing, we will be one hand, one voice and not betray each other."

Fox News' Ian McCaleb, Major Garrett, Mike Emanuel, Rick Leventhal, Eric Shawn and Liza Porteus and The Associated Press contributed to this report.