The officials taken into custody - all on the U.S. most-wanted list of 55 regime leaders - were identified as Abdel Tawab Mullah Huweish, director of the Military Industrialization Organization; Taha Muhie-eldin Marouf, a vice president and member of the Revolutionary Command Council, and Mizban Khadr Hadi, another Revolutionary Command Council member who had been an adviser to Saddam since the early 1980s. 

The Military Industrialization Organization oversaw development of Iraq's most lethal weapons and Huweish's detention could add to investigators' knowledge of any programs aimed at producing chemical, biological or nuclear weapons. 

Huweish was listed as No. 16 on the most-wanted list, Hadi was No. 41 and Marouf was No. 42. Eighteen of the 55 officials on the list are now in custody, and another is believed to have been killed in an air strike. 

Even with President Bush declaring an end to "major combat operations," the raid on regime loyalists in Saddam's hometown of Tikrit was the latest of many signs that daunting challenges remain for American forces in Iraq. 

Almost daily, U.S. troops exchange gunfire with Iraqis, sometimes as a result of anti-American protests. Lawlessness is rampant, in a land abounding with well-armed citizens and divided loyalties. 

Tikrit, the stronghold of Saddam's al-Tikriti clan, has been a center of pro-regime sentiment even as the former government collapsed. U.S. officers say members of Saddam's Baath Party are trying to reorganize to stage attacks on American troops, and one of the men detained Friday was described as a party official. 

"Some of these guys are continuing to terrorize people out there, and that's going to take a while to work through," said Lt. Col. Phil Battaglia, commander of the infantry regiment that conducted the raid. 

During the raid, troops found several weapons and about $3,000 hidden in various houses, and one Iraqi was killed when he tried to wrest a rifle from an American soldier, U.S. officers said. 

The raid, the second in Tikrit in as many days, began shortly after midnight when six Bradley Fighting Vehicles sealed off a residential district. Soldiers broke down gates and doors, forced their way inside and emerged with about 20 men, blindfolded and hands tied behind their backs. 

The U.S. military provided few details about the detention of the three top officials. The Army said Hadi was captured Thursday in Baghdad, but it was not immediately disclosed whether Marouf and Huweish were captured or surrendered. 

Marouf was the only Kurd in the Baath hierarchy. He was appointed as one of Iraq's two vice presidents in 1975, but the position is seen largely as a gesture to the Kurdish minority and he had little real power. 

Hadi, who had been promoted by Saddam in March to command military defense in the area that included the Shiite Muslim holy cities of Karbala and Najaf. He has been a minister without portfolio since 1982 and was decorated by Saddam for his services during the 1991 Gulf War and a monthlong Shiite rebellion that followed Iraq's defeat. 

In Najaf, police arrested two people Friday after gunmen shot automatic weapons and threw grenades outside the city's central shrine, the tomb of Imam Ali. Authorities said it was probably common crime, but some clerics blamed former Baath Party operatives. 

The men arrested were later identified as two of the 16 suspects in the killing of Abdul Majid al-Khoei, a cleric hacked to death by a mob April 10 at the tomb. 

Al-Khoei's slaying was widely perceived as part of an internal dispute among Shiites, and many worried it heralded a threat to the restoration of order in Iraq. He was killed along with rival cleric Haider al-Kadar at an appearance that was to have been a sign of reconciliation. 

Shiites, who are a majority in Iraq, were oppressed under Saddam's predominantly Sunni Muslim regime. 

No new violence was reported Friday in Fallujah, where seven U.S. soldiers were wounded Thursday in a grenade attack. 

That attack was in apparent retaliation for U.S. gunfire earlier in the week that killed 18 people, according to local hospital officials. U.S. officers said their soldiers were defending themselves after being shot at, while residents said the victims were unarmed protesters. 

Even a leader of the temporary city administration spoke harshly of the U.S. troops in Fallujah, a Baath Party stronghold 30 miles west of Baghdad. 

"After the massacre, we don't believe the Americans came to free us, but to occupy and take our wealth and kill us," said Mohammed Farhan, who is in charge of city security. 

Bush, in his speech Thursday aboard an aircraft carrier returning from the war, said much still needed to be done in Iraq, including restoring order, establishing a democratic government, tracking down Saddam and his top aides, and finding weapons of mass destruction. 

Thus far, the U.S. government has rejected proposals to let United Nations weapons inspectors assist the U.S. teams that are searching Iraq for chemical, biological and nuclear weapons. 

However, other U.N. staff have returned to Baghdad for the first time since the war to assess emergency humanitarian needs. A 21-member team that arrived Thursday included representatives of the World Health Organization, the World Food Program, the U.N. Children's Fund and the U.N. Development Program.