President Bush was briefed Wednesday on the spiraling violence and U.S. casualties in Iraq where American forces are facing the heaviest fighting since the fall of Baghdad a year ago.

Bush, at his ranch in Crawford, Texas, through Easter Sunday, got an update on fighting by U.S. Marines in the Sunni Muslim stronghold of Fallujah. Bush spoke via a secure video conference call with his national security advisers. The call was to have included Gen. John Abizaid (search), commander of the Central Command which has jurisdiction in Iraq, and L. Paul Bremer (search), the top U.S. civilian in Iraq.

Bush also spoke by telephone for 30 minutes with British Prime Minister Tony Blair (search), his closest ally in Iraq. The two leaders will meet in Washington late next week to discuss Iraq and other foreign policy problems.

Wednesday's briefing was a follow up to a conference call Tuesday night among the president, Defense Secretary Donald Rumsfeld (search), Air Force Gen. Richard Myers (search), chairman of the Joint Chiefs of Staff, national security adviser Condoleezza Rice (search) and White House chief of staff Andy Card.

As the security situation in Iraq remains dangerous, a U.S. official speaking on the condition of anonymity said that a variety of elements are conducting the attacks in Iraq, including Shiites and members of the fallen Baathist regime, a group that is thought to incorporate former Iraqi military or intelligence figures.

A defense official, also speaking on the condition of anonymity, said there is no indication that there's a popular uprising from a Shiite monolith. For instance, radical Shiite cleric Muqtada al-Sadr does not have a large following and his militia — the Al-Mahdi Army — only numbers perhaps in the thousands, the official said.

This official also said the military is making progress in places including Ramadi, where 12 Marines were killed late Tuesday.

The Marines died in heavy fighting, part of an uprising involving both Sunni and Shiites that now stretched from Kirkuk in the north to the far south. Rumsfeld said on Tuesday that if violence gets worse, U.S. military commanders will get the troops they need to deal with it.

On Capitol Hill, a senior Democrat, Sen. Robert Byrd of West Virginia, urged caution.

"Surely I am not the only one who hears echoes of Vietnam in this development," Byrd said. "Surely, the administration recognizes that increasing the U.S. troop presence in Iraq will only suck us deeper, deeper into the maelstrom, into the quicksand of violence that has become the hallmark of that unfortunate, miserable country."

"Starkly put, at this juncture, more U.S. forces in Iraq equates more U.S. targets in Iraq," Byrd said. "The harsh reality is this: one year after the fall of Baghdad, the United States should not be casting about for a formula to bring additional U.S. troops to Iraq. We should instead be working toward an exit strategy."

Sen. Chuck Hagel, a Republican member of the Foreign Relations Committee, said the United States and its allies are "right on the edge" of losing control in areas of Iraq.

On CNBC television's Tuesday night program, "Capital Report," Hagel said the current situation was "dangerous, complicated and I think we're on the verge of seeing, in some of these areas, of seeing some of the progress we've made over the last year come undone."

Hagel said that Abizaid is seriously considering whether more troops are needed. "And if he decides that's what we need, we need those troops in there, we need them now," the Nebraska Republican said.

"This is a crucial, critical time. We cannot allow some of these areas to become uncontrollable..," he said.

Senate Minority Leader Tom Daschle, D-S.D., said he thinks Bush "needs to produce a plan to show what we are transitioning to."

Presumptive Democratic presidential nominee John Kerry criticized the administration Wednesday for deciding at a relative early juncture to set the June 30 target date for transferring sovereignty back to the Iraqis and said Bush has yet to explain to whom power in Iraq would be delivered.

"You don't set an arbitrary date for the transfer of power to a non entity. You have to make the judgment of stability. I mean, this date it, appears to me, may well have been set by the American election, not by the stability of Iraq," Kerry said in an interview with American Urban Radio.

"Where are the people with the flowers, throwing them in the streets, welcoming the American liberators the way Dick Cheney said they would be?" Kerry said. "This is one of the greatest failures of diplomacy and failures of judgment that I have seen in all the time that I've been in public life."