ROBERT SIEGEL, host:

Now what the Pentagon really thinks about troop levels in Iraq and getting US forces out. It's been the most contentious topic in Washington ever since Representative John Murtha, a generally hawkish Pennsylvania Democrat, said the US should start pulling back.

Representative JOHN MURTHA (Democrat, Pennsylvania): I believe before the Iraqi elections scheduled for mid-December, the Iraqi people and the emerging government must be put on notice: United States will immediately redeploy.

SIEGEL: Well, Republicans and administration figures all the way to President Bush pounced on Murtha, insisting the US will stay the course.

President GEORGE W. BUSH: One of our top commanders in Iraq, Major General William Webster, says setting a deadline for our withdrawal from Iraq would be, quote, "a recipe for disaster." General Webster's right.

SIEGEL: So what is the course the US is staying? If the administration wants to draw down troops, if Iraqi leaders themselves say they want a timetable and if Congressman Murtha's timetable is too rapid, then what does the Pentagon think about US troops coming home? Well, Washington Post military affairs reporter Bradley Graham writes about this today.

And, Bradley Graham, let's start with how many troops or brigades the US now has in Iraq.

Mr. BRADLEY GRAHAM (The Washington Post): US now has about 18 combat brigades, and with supporting troops--headquarters staff and so on--that brings the total to something over 150,000.

SIEGEL: And in 2006, what do people at the Pentagon see happening to those numbers?

Mr. GRAHAM: There are a number of different scenarios; the plan is very flexible. But it is essentially a plan for drawing down forces, something under 100,000 equal to about 10 combat brigades by the end of the year. That is what officers describe as the `moderately optimistic scenario.'

SIEGEL: Is there a more pessimistic scenario than that?

Mr. GRAHAM: There sure is. The most pessimistic would be to keep levels pretty much where they are.

SIEGEL: I want you to answer a key question about a principle at work here. Does the Pentagon regard crushing the Iraqi insurgency as a milestone to be passed before there's a big US pullout, or does the US now assume that it will bequeath a counterinsurgency effort that'll still be necessary after the US leaves--bequeath it to Iraqi forces?

Mr. GRAHAM: US commanders gave up long ago thinking that US forces alone could defeat the insurgency. For many months now commanders in Iraq have been saying that the insurgency can only be solved with a political solution, and their main objective has been to try to keep it in check, to try to contain it while they build up Iraqi security forces. They feel now that those forces are at a point where US forces can begin a gradual reduction sometime early next year.

SIEGEL: You actually write about, well, what amounts to virtually a formula for improvements in the number of Iraqi units and the drawdown in US units that we might see in exchange. How do they view that there?

Mr. GRAHAM: There is this very rough rule of thumb, as one officer described it, that says that for every three Iraqi battalions and one Iraqi brigade headquarters that reach a readiness level of two, the US might consider drawing down one US battalion. Now a readiness level of two is on a scale of one to four, with one being the best. And two means that an Iraqi unit is capable of taking the lead in a counterinsurgency operation but will still require US support.

SIEGEL: And how do Iraqi forces rate right now in terms of units that could be described at a readiness level of two?

Mr. GRAHAM: About 36 Iraqi battalions, and an Iraqi battalion's about 7 or 800 troops. The idea is once they're good enough to at least be able to take some initiative and take the lead in operations, some US forces can begin to withdraw. And US commanders believe they are at that point now with at least some units.

SIEGEL: If, in fact, there is the reduction in 2006 that you've described, would the nature of what US troops who are deployed in Iraq--would it be radically different from what they were doing, say, a year ago?

Mr. GRAHAM: Yes. The mission of US forces in Iraq has been evolving from one initially focused on counterinsurgency operations to one, even this past year, that began to shift more to building up Iraqi security forces, mentoring those forces, advising those forces, so that by the time we get to 2007, assuming this steady downward glide path can hold, there'll be very few actual US combat forces in Iraq, and instead the predominant number--kinds of forces that we'll have there will be support, logistics, intelligence, aviation kinds of units.

SIEGEL: That's Washington Post military affairs reporter Bradley Graham.

And, Bradley Graham, thanks a lot for talking with us.

Mr. GRAHAM: Thank you. Transcript provided by NPR, Copyright NPR.