THE DEBATE BEGINS.

It includes how large the Army should be. But that answer comes only after a host of other questions have been answered.

You can bet the Pentagon planners are pulling all nighters on this one.

Mr. Rumsfeld has been telling Congress in recent days that before the Pentagon takes the major step of asking for money to enlarge the military, he hopes to cut back on less urgent foreign assignments, to move people in uniform out of administrative tasks and back into combat units and to change the balance of assignments between active-duty forces and those in the National Guard and Reserves.

A senior adviser to the defense secretary said that while it was easy enough to identify how many Army or Marine Corps troops the Pentagon needed for the global campaign against terror and for extended tours of duty on the ground in Iraq, Mr. Rumsfeld made no final decisions over the weekend. He waits for a larger blueprint from the military that would make new troop rotations more predictable.

"We are not fighting in a knife fight here — we're looking out long term," said one Pentagon official involved full time in planning force rotations for Iraq.

But the military is struggling with what another Pentagon planning official called "the tyranny of fixed numbers," which is especially critical for the Army.

Of the Army's 33 active-duty combat brigades, only three are described as free now for a new mission: the Stryker Brigade Combat Team at Fort Lewis, Wash., built around a new, lightly armored vehicle called Stryker; a brigade of the First Infantry Division at Fort Riley, Kan.; and a brigade of the 82nd Airborne Division that returned to Fort Bragg, N.C., from Afghanistan six months ago.

Twenty-one brigades are now assigned overseas — 16 of them in Iraq. Of those not abroad, most are already earmarked as replacement forces for other missions, like the one in Afghanistan, are rebuilding their ranks or are on emergency standby in case of a crisis with North Korea.

Officials said the National Guard and Reserves, which as of Wednesday had 201,099 members on active duty, would probably have to shoulder some of the burden of any additional missions as well.

The Marine Corps could also be asked to share long-term peacekeeping duties, which traditionally have fallen to the Army.

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