Washington ? Amid growing indications that some of the attacks against U.S. soldiers in Iraq are organized and coordinated, the chief civilian administrator and Army officers on the ground would like an increase of as many as 50,000 new troops in the theater, according to knowledgeable sources.

At a White House ceremony Tuesday honoring those re-enlisting in the armed services, President Bush gave no indication that he was considering ordering new troops to Iraq and pinned some of the responsibility for recent attacks on terrorists.

New attacks against American forces wounded at least six soldiers Tuesday, and U.S. troops shot and killed four people at checkpoints. A mosque explosion killed 10 people in Fallujah — further stirring anti-American sentiment in a town where Saddam and his Baath Party still enjoy support.

A possible request by U.S. administrator Paul Bremer for the additional troops was discussed at a National Security Council meeting several days ago and the White House has indicated it would be reluctant to agree to such a large increase, the sources said.

Bremer’s request underscores just how difficult it has been for his small civilian staff and some 158,000 U.S.-led troops to meet the demands of Iraqis.

It also conflicts with upbeat public statements from President Bush, Defense Secretary Donald Rumsfeld and Bremer himself on the progress made in Iraq.

In Baghdad, Bremer said the U.S.-led provisional authority was “well on track to establish an Iraqi interim administration by mid-July.”

Bremer also said the U.S.-led authority had asked airlines to submit applications to resume commercial service to Baghdad.

“Day by day, conditions in Iraq continue to improve,” Bremer said.

Despite his reassurances, a burgeoning insurgency has seen several attacks on U.S. troops every day, leading some to worry about the possibility of a Vietnam-style political and military quagmire.

In Washington, President Bush said Tuesday that anti-American violence was expected, because Saddam loyalists will stop at nothing to regain power.

“These groups believe they have found an opportunity to harm America, to shake our resolve in the war on terror, and to cause us to leave Iraq before freedom is fully established,” Bush said. “They are wrong, and they will not succeed.”

In Tikrit, Abdullah Mahmoud al-Khattab, who was leader of Saddam’s Bani al-Nasiri tribe, was shot and killed Sunday afternoon while he rode in his car.

Gov. Hussein al-Jubouri said al-Khattab’s son, Odai, also was wounded when assailants fired from a pickup truck and fled the scene.

Al-Khattab “had many enemies, and he had confiscated a lot of properties and killed many people,” the governor said, adding, “The person who killed him could have taken revenge.”

Several Tikrit residents said the killers could have been Saddam loyalists angered at the tribal leader’s public disavowal of the ousted dictator.

Most other Iraqis express disdain for Saddam, yet anti-U.S. forces have persisted in stepping up attacks on occupation forces in recent days.

Americans attacked

On Tuesday, assailants traveling in a vehicle in central Baghdad fired a rocket-propelled grenade at a U.S. military vehicle, wounding three soldiers. A grenade slammed into a U.S. truck on a road 12 miles south of Baghdad, injuring three soldiers.

In western Baghdad, U.S. troops shot and killed two people when their car didn’t stop at a checkpoint, witnesses said. A U.S. military spokesman said he had heard about the incident but could not confirm it. Later, two civilians were shot and killed at another checkpoint, one by soldiers who feared he was an insurgent and another by a stray bullet, witnesses said.

Blast stirs resentment

In Fallujah, a blast in a cinderblock building in the courtyard the al-Hassan mosque killed 10 Iraqis and wounded four late Monday, said Col. Guy Shields, spokesman for the U.S. military in Baghdad. Iraqis insisted the blast was caused by a U.S. missile — an account the military denied.

After the explosion, dozens of people gathered around the site shouting anti-American slogans.

“There is no God but Allah, America is the enemy of God,” they chanted.