America's top soldier in Iraq said Tuesday a "blanket of fear" that Saddam Hussein (search) will return prevents Iraqis from giving U.S. troops intelligence vital to curb the growing insurgency -- stepped up attacks underlined by a late night barrage on the heart of Baghdad.

The top U.S. administrator in Iraq abruptly departed for Washington, amid growing frustration over the inability to halt the attacks on U.S. soldiers and the slow process of turning power over to the Iraqis.

Late Tuesday, insurgents fired mortars toward the U.S. headquarters compound, known as the "Green Zone," in Baghdad. The Coalition Provisional Authority (search) said there was no damage to coalition headquarters, located in the Republican Palace. After one detonation, white smoke could be seen rising from an area just north of the palace.

Despite the mounting violence, Lt. Gen. Ricardo Sanchez (search) angrily dismissed comparisons between Iraq and Vietnam and said his soldiers will try to balance between the use of massive firepower and the need to win the goodwill of Iraqis. Attacks on coalition forces, he said, now average 30 to 35 a day, twice the number two months ago.

"On the near term, given the focus we have on our offensive operations, and given the level of engagements that the enemy has chosen to move to ... we are going to have more attacks here in the next 30 to 60 days," Sanchez told reporters.

L. Paul Bremer, the chief civilian administrator for Iraq, returned to Washington at a time of increasing tension between coalition officials and the U.S.-appointed Iraqi leadership, the Governing Council. Bremer wants to delay transferring sovereignty until the Iraqis draft a constitution and hold national elections.

As Bremer held meetings at the White House on Tuesday, a Bush administration official acknowledged concerns about the council's progress since its installation four months ago. But he rejected suggestions the administration was about to put the council out of business.

President Bush's national security advisers questioned Bremer on Tuesday about how to break a political logjam in Baghdad and speed planning for the nation's political future.

Bremer attended the White House meeting with Secretary of State Colin Powell, Defense Secretary Donald Rumsfeld, National Security Adviser Condoleezza Rice and other key officials.

There have been concerns about the performance of the governing council, a senior administration official said, particularly the lack of progress toward a Dec. 15 deadline to set a timetable for writing a new constitution and holding democratic elections.

The Iraqis have yet to agree on how to choose delegates to draw up a constitution. Some coalition officials suspect the Iraqis are stalling in hopes Bremer will quickly give them more power.

Some Iraqi council members are also pushing for an Iraqi-controlled paramilitary force to fight the insurgents, something Bremer opposes without coalition oversight and control.

The White House talks were part of a process to accelerate political, military and especially security arrangements in Iraq, officials said.

"The long-term security of Iraq will be assured by the Iraqis themselves," Bush said. He said 118,000 Iraqis were serving as police officers and in other security positions, and 35,000 Iraqi troops would be in the field by the end of next year.

Coalition sources said Bremer is increasingly frustrated by some members of the Governing Council.

U.S. soldiers have been killed on average of one every 36 hours since Bush declared an end to major combat operations on May 1.

Sanchez said insurgents have changed tactics to inflict more damage and casualties on American troops while reducing their own.

"I think we have got to be realistic," he said when asked if the insurgency was worsening. "The enemy has evolved its tactics. They use mortars and rockets so as not to engage our forces."

However, he said U.S. forces intended to "get pretty tough" against the insurgency.

"The stark reality is that, militarily, they cannot defeat us, and they know it, and I remain supremely confident in this reality," he said.

"It is not Vietnam," Sanchez snapped when asked whether Iraq resembled the early days of that conflict. "And there is no way you can make the comparison."

Some military experts cautioned that use of overwhelming firepower against the resistance may prove deadly for civilians at a time when Washington is trying to gain favor among Iraqis.

In Samara, 60 miles north of Baghdad, some Iraqis complained insurgents were launching attacks from residential areas, and that the American response kills and injures innocent civilians.

"It's everyone's right to resist the occupation, but they shouldn't attack from residential areas, from between houses," said Qahtan Karam, a Kurd whose mother was killed and whose wife was seriously wounded in an exchange of fire Oct. 24 in Samara.

Sanchez also said he believed about 200 foreign fighters were active in Iraq, in many cases cooperating with local insurgents, and that the military at one time held about 20 suspects believed linked to Osama bin Laden's al-Qaida terror network.

"But as we have continued to refine and interrogate, we have not been able to establish definitively that they were al-Qaida members," he said. Foreign fighters, he said, were using two routes across the Syrian border and one from Iran.

Sanchez said intelligence obtained by his troops on the insurgents has improved recently, but stressed that a network of human intelligence was needed to give U.S. forces access to guerrilla cells and their operational structures.

The capture or killing of Saddam, he added, would "relieve the people of Iraq from the fear of him returning and that blanket of fear that exists is keeping some Iraqis from cooperating and focusing on the future.

"If we could eliminate this fear and they know that that regime will not return, then I think we will get a lot of cooperation," he said.

Fears of reprisals by Saddam loyalists or Muslim militants, together with heading off the stigma of being labeled collaborators are thought to keep Iraqis from cooperating with the Americans.

Sanchez was repeatedly asked to elaborate on remarks attributed to Gen. John Abizaid, chief of the U.S. Central Command, that the military will use stern measures unless attacks against U.S. forces were curtailed. Abizaid spoke to tribal sheiks and mayors during the weekend.

Hours after Abizaid's warning, U.S. jets dropped three 500-pound bombs near the city of Fallujah after three U.S. paratroopers were wounded in an ambush. On Friday, bombs were dropped on the outskirts of Tikrit, Saddam's hometown, after a U.S. helicopter was apparently downed, killing six soldiers.

Asked why the U.S. military was dropping bombs now, Sanchez said: "Because that is the combat power necessary to defeat the enemy and send a very clear signal that our intent is to defeat the former regime loyalists, the terrorists and those people that are attacking the coalition and the Iraqi people."

"The most important message," he continued, "is that we are going to get pretty tough ... but we will do everything possible to minimize the impact on the people of the country."