With all the attention focused on President Bush's likely announcement this week that additional American troops would be sent to Iraq, what has not generated as much attention is the possibility that some units already in Iraq could see their tours of duty lengthened, while their expected replacements would be used to provide the additional troops in Baghdad.
While those extensions are possible, ABC News has learned that the Pentagon is considering a separate request from Marine commanders in Iraq to extend the tour of duty of 2,200 Marines currently serving in the dangerous al Anbar province.
The Marines and sailors of the 15th Marine Expeditionary Unit were ordered to Iraq in mid-November while in the middle of a routine six-month overseas deployment.
With the unit's deployment scheduled to end in February, the senior Marine commander in Iraq, Maj. Gen. Richard Zilmer, has asked that the 15th Marine Expeditionary Unit have its tour of duty extended.
Marine spokesman Lt. Col. Bryan Salas says Zilmer requested the extension to build "on the momentum the unit has generated and the good work they've done."
It is not clear how long the extension would last. Any extension would have to be approved by Defense Secretary Robert Gates.
The request was first reported by the military newspaper Stars and Stripes.
In the three years since the invasion of Iraq, only a small number of military units that have served in Iraq have seen their tours of duty extended. Army units serve one-year deployments to Iraq; Marine units deploy generally for seven months.
The issue is politically sensitive as military planners weigh the needs of the battle front and the expectations of service members and their families to stick to the deployment schedules.
Last year, former Defense Secretary Donald Rumsfeld witnessed firsthand the results of those expectations following the four-month extension of Alaska's 172nd Stryker Brigade.
Rumsfeld flew to Alaska for an angry meeting with family members. That last-minute extension was particularly painful to the families as some members of the unit had already returned home.
Marine officials say the 15th Marine Expeditionary Unit serving in western al Anbar province near the Syrian border has improved the security situation in the province's roadways where insurgents hijack vehicles or kidnap residents for ransom.
Officials add there has been "significant progress" in al Anbar over the last 60 days in getting Sunni sheikhs to agree to cooperate with the coalition.
One indicator of that progress has been the sizeable increase in the number of police recruits in the area.
Just last month, 1,000 new police recruits signed up in the province, as to the 30 or so new recruits in prior months. Six hundred of the recruits came from violence-ravaged Ramadi, and the recruiting numbers are expected to remain high again this month.
The surge will be a combination of adding more brigades on top of existing units already in Iraq.
Pentagon planners have reportedly presented President Bush with a proposal to initially send two combat brigades directly to Baghdad to improve the security situation there.
An additional two or three combat brigades would be sent later through April and May as needed. An army brigade usually consists of 3,500 to 5,000 soldiers.
Adding these brigades would mean 20 combat brigades in Iraq, providing the 20,000 additional troops.
There are currently an estimated 132,000 American service members in Iraq.
If a surge was ordered, the first two brigades likely to be sent to Baghdad would be units that already had deployment orders to the Middle East.
These include a brigade from the 82nd Airborne Division based at Fort Bragg, N.C., and a brigade from the 3rd Infantry Division based at Fort Stewart, Ga.