STEVE INSKEEP, host:
It's MORNING EDITION from NPR News. I'm Steve Inskeep.
DEBORAH AMOS, host:
And I'm Deborah Amos. Senators John McCain and Barack Obama don't agree on much, particularly when it comes to Iraq. But they have found common ground when it comes to Afghanistan.
Senator JOHN MCCAIN (Republican, Arizona, Presidential Candidate): Our commanders on the ground in Afghanistan say that they need at least three additional brigades.
Senator BARACK OBAMA (Democrat, Illinois, Presidential Candidate): I will send at least two additional combat brigades to Afghanistan.
AMOS: The presidential candidates agree. President Bush, top military commanders, and members of Congress also agree. More troops are needed in Afghanistan. But without an immediate reduction in U.S. forces in Iraq, there won't be a surge of troops in Afghanistan anytime soon. NPR's defense correspondent Guy Raz reports.
GUY RAZ: When Senators McCain and Obama pledge to send more brigades to Afghanistan, they're talking about combat troops. A brigade, or its Marine equivalent, is made up of around 5,000 troops.
Now, even if a President McCain or Obama wanted to send more of these brigades to Afghanistan tomorrow, he'd have a hard time making it happen.
Mr. JACK KEANE (Former Army Chief of Staff): The problem is, there are no units available that aren't designated.
RAZ: This is Jack Keane, the Army's former vice chief of staff. What he means is that the Army and Marine Corps are still operating at maximum capacity.
Here's roughly how it works: Between the Army and Marines, there are about 50 brigades or regiments - teams that do combat operations. As retired General James Marks explains, more than a third of these units are now deployed, mostly to Iraq.
General JAMES MARKS (U.S. Army): Every unit, every brigade combat team, is engaged in the fight in Southwest Asia in one way or another. It's either coming from or it's going to or getting ready to go to one of those two locations.
RAZ: The formula for how the Army fields combat units is fairly simple.
Professor LEONARD WONG (Army War College): It takes to send one brigade really three brigades.
RAZ: Leonard Wong is a professor at the Army War College in Carlisle, Pennsylvania.
Prof. WONG: It takes three brigades, because you have the unit that's deployed, but you also have a unit that's training to deploy, and a unit that's recovering from deployment.
RAZ: This means that even though the Army and Marine Corps have more than 50 brigades between them, only about 18 can be deployed at any given time. Beyond that number would mean longer tours of duty and less time to recover and retrain at home.
Right now there are about five times more U.S. troops in Iraq than in Afghanistan. So if the president wanted to beef up the numbers in Afghanistan before the end of the year, he'd most likely have to reduce them in Iraq.
There are a few complicating factors. For one, says retired General James Marks, most brigades now getting ready to deploy are training for Iraq.
Gen. MARKS: There certainly is very specific preparation that you want that unit to go through before they deploy to a very specific location. So there is what I would call Iraq-specific training and there is Afghanistan-specific training.
RAZ: So for example, if a brigade was scheduled to go to Iraq say this November, the president could simply divert that unit and send it to Afghanistan instead. The problem is the brigade would then have to extend its training by a few weeks to study Afghanistan-specific intelligence and terrain. By the time the unit arrived, it would be early December, and in that time frame, says Jack Keane, the troops wouldn't have an immediate impact.
Mr. KEANE: It wouldn't be in time for the so-called fighting season that takes place in the spring and summer.
RAZ: Afghan winters are generally quieter, and so Keane believes any possible troop surge in Afghanistan is likely to start in March or April of next year. But for that to happen, President Bush would most likely have to reduce or commit to reduce the number of brigades in Iraq before the end of this year. And Jack Keane, who also helped plan 2007's Iraq surge, says there's a risk in doing that as well.
Mr. KEANE: These are hard-fought gains that we have arrived at in Iraq. And we do not want to squander these gains in our haste to move forces to Afghanistan.
RAZ: But the combination of political pressure and broader public support for the Afghanistan campaign over Iraq means that 2009 is almost certainly set to become the year of the Afghan surge.
Guy Raz, NPR News, Washington.