Carried out by the Army's Fourth Infantry Division and Task Force Ironhorse, the raids involved thousands of soldiers and hundreds of tanks and armored vehicles. Army officials arrested more than 60 people, and seized several caches of weapons and documents.

But military officials said they did not capture anyone on their list of most-wanted Iraqis, and the relative absence of armed resistance suggested that they had not uncovered any major pockets of resistance. 

Army commanders said they had staged more than 20 raids over a vast part of the Tigris River valley, beginning just north of Baghdad and going upriver beyond the city of Tikrit. There were no reports of American casualties in the raids, which are likely to continue in the days to come.

Today's almost simultaneous raids began around 2 a.m., and struck homes, farms and abandoned buildings that were suspected of housing loyalists to Saddam Hussein or other groups fighting the American-led occupation.

"We want to send a message of `Don't mess with us,' " said Lt. Col. Aubrey Garner, commander of the First Battalion, 68th Armor, which is part of the Fourth Infantry Division. 

"They will see that we have the flexibility to bring firepower," he continued, wherever and whenever. "The ability is almost magical."

In raids about 40 miles north of Baghdad, the battalion seized more than a dozen weapons from pistols to assault rifles and ammunition.

Colonel Garner's battalion also arrested three men, including a member of Iraq's former military intelligence service named Amir Ismael Muhammad. 

Mr. Muhammad was found with five different identity cards, and the house he was in contained technical publications on missile guidance systems and printouts of an Internet search on weapons production, according to the American military. 

The Associated Press reported that soldiers in another raid nearby had arrested a man suspected of recruiting Iraqis to attack Americans. 

Tanks and armored trucks surrounded each of the areas being raided, and sometimes blocked off roads leading to them. Airplanes also provided support, dropping flares carried on parachutes that provided just enough light to let soldiers see with night-vision goggles. 

The sweeps were focused most intensively on the areas north of Baghdad that have been staging grounds for an accelerating stream of deadly hit-and-run attacks on American troops. Similar raids were carried out for several days beginning almost two weeks ago. 

The attacks on American and British troops have reached a new intensity in the last week, killing more than a half-dozen American soldiers in Baghdad and central Iraq. Among the victims were two American soldiers kidnapped in their Humvee near here; their bodies were found this weekend. 

Other victims included a soldier who was shot in the head at point-blank range while shopping at an outdoor market in Baghdad on Friday. There have also been numerous ambushes of Americans using rocket-propelled grenades and remotely-detonated bombs.

L. Paul Bremer III, the Americans' top civilian administrator in charge of Iraq, said tonight that he was "certainly not panicked" by the attacks and that Americans had in the last two weeks begun receiving tips from Iraqi citizens.

"Plain old citizens are now confident enough that they are willing to provide us with information," Mr. Bremer said in a meeting with reporters tonight. "Most of it is pretty good."

But it is not clear that today's raids produced much in the way of concrete results. Unlike a similar set of raids earlier this month, the ones today did not lead to any major fire fights. All told, military officials said in a statement released tonight, soldiers seized only 14 Kalashnikov assault rifles, two shotguns and an unidentified amount of ammunition.

The two raids carried out by the First Battalion, 68th Armor, did produce tantalizing hints of militant activity, as well as of people who might remain loyal to the Baath Party of Saddam Hussein.

But the raids did not uncover what intelligence officials had been hoping to find. One raid, against a compound that had at one time been used by the Badr Brigade, a Shiite militia groups, turned up little more than two families of squatters. 

In a second raid on a farmhouse several miles south of here, officials had been hoping to capture a high-ranking intelligence officer named Col. Asad Adeen. 

Soldiers quickly rounded up 14 men in three buildings, handcuffed them and covered their heads with sacks to keep them disoriented. 

An extensive search produced a large trove of papers about missile-guidance systems and other military technology, one of which had been written by Colonel Adeen, the intelligence officer. Soldiers also found handguns and five assault rifles, including two being hidden by women under their bed blankets.

But the colonel himself was nowhere to be found. Arabic-speaking interrogators then questioned the men until well after dawn. But the American commanders ultimately decided to release 11 of the 14 men, including a relative of Colonel Adeen, saying there was no evidence they were involved in either the Baath Party or guerrilla attacks.

"The target was Adeen, not these other people or members of his family," Colonel Garner said. 

The raids this morning appeared to be the start of a campaign that will continue in the days and weeks to come. In the last big sweep, two weeks ago, 497 assault rifles and 124 rocket-propelled grenades, among other weapons and ammunition, were confiscated.

Meanwhile, attacks on American troops continued today. Two soldiers were wounded and an Iraqi civilian was killed after coming under attack while in a convoy on a road leading to Baghdad International Airport, the military said.