ARLINGTON, Va. — Insurgents are planning to use car bombs and improvised explosive devices early in the fight for Fallujah, then retreat into the labyrinthine city center and fight house- to-house, the top U.S. commander in Iraq said Monday.

Gen. George W. Casey Jr., who is commander, Multi-National Force-Iraq, spoke from Baghdad via telephone to Pentagon reporters just hours after the long-anticipated main assault on the city began.

Casey refused to say precisely how many coalition fighters are involved in the Fallujah operation, but admitted that one reporter’s estimate of 15,000 was “in the right ballpark.”

Included in the fight are U.S. soldiers and Marines, as well as Iraqi forces and the United Kingdom’s Black Watch Regiment, which is “working along western bank of Euphrates River to disrupt [insurgent fighters’] movements towards Baghdad,” Casey said.

How many opponents they will face remains unknown, Casey said.

“We’ve been watching this fairly closely,” Casey said. “I think there are people who have moved out; I think there are people who have moved in.”

Yet even though “I don’t have a specific number on the number of enemy who have left; I expect we will have a fight in there over the next few days,” Casey said.

Insurgents are armed with “a range of weapons,” Casey said, including AK-47 semi-automatic weapons, machine guns, rocket-propelled grenades and some anti-aircraft weapons.

However, the insurgents’ “weapons of choice are improvised explosive devices and car bombs,” Casey said.

“Our [intelligence analysts] tell us they [the insurgents] have lined the streets with IEDs,” Casey said.

Coalition forces also as “expect them to come at us with car bombs,” Casey said.

“What we generally see is an outer crust of defense,” Casey said. Then the insurgents “will fall back into the center of the city, where there will be a major confrontation.

In his first appearance before the Pentagon press corps since well before the elections, Defense Secretary Donald Rumsfeld said Tuesday that unlike April’s unsuccessful attempt to take control of Fallujah, this battle would “absolutely” finish the job.

“I cannot imagine [the battle in Fallujah] would stop without being completed,” he said.

But when asked whether the fall of Fallujah would so discourage other insurgents looking for safe haven in Iraq that they would finally give up the fight, Rumsfeld said, “I wouldn’t use the word ‘final’,” to describe the battle.

Defeating insurgent forces in Iraq “is a tough business and it’s going to take time,” Rumsfeld said. “I wouldn’t suggest this one city [Fallujah will be] the last step in this process.”

However, he added, “Over time a process of tipping will take place. More and more Iraqis will be angry [at the lack of a security in their country] and I think they will turn on [the insurgents].”

Casey said that he has not heard reports by an embedded National Public Radio reporter that said one Iraqi unit that was supposed to fight shrank by 500 men who resigned their positions over the weekend.

However, Casey added, he had received information that some fighters who were supposedly on leave and expected to show up for the fight, did not do so.

Rumsfeld called the reported loss of Iraqi fighters “as an isolated problem,” citing participation by other units in recent fights in Najaf and Samarra.

“The easy thing to do is recruit people and train people,” Rumsfeld said. “The hard stuff is developing noncommissioned officers” and other key leaders.”

Until that happens, Rumsfeld said, is that “what one ought to expect from time to time we’re going to see this kind of thing.”

And regardless, Casey said, any loss of Iraqi fighters would not impact the Fallujah fight.

Meanwhile Rumsfeld refused to respond to questions about whether he would remain for at least part of President Bush’s second term, as he is widely expected to do.

Although he said he has “met with [Bush] two or three times on totally different subjects since the election,” the prospect of his remaining in the cabinet “hasn’t come up in those discussions.”

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