Senior officials at the Pentagon are calling reports about a proposed shifting of 25,000 Marines from Iraq to Afghanistan next spring very preliminary thinking and not policy.

The proposal would be to give Marines ownership of operations in Afghanistan, which is led by NATO, and to turn Iraq over to the Army.

Asked about the idea on Thursday, Defense Secretary Robert Gates, who is traveling in Europe, said he isn't prepared to make any announcements, but it is a suggestion being considered.

"I have heard that there were beginning to think about that, and that's all that I've heard. I've seen no plan; no ones come to me with any proposals about it. My understanding is that its, at this point, extremely preliminary thinking on the part of perhaps some staff people in the Marine Corps, but I don't think at this point it has any stature," Gates said.

Some defense officials have argued it would allow the services to operate more efficiently by focusing their manpower and energy. If Marines shift to Afghanistan, then the Army could focus on troop rotations in and out of Iraq.

Marine Corps commandant James T. Conway pitched the idea to Adm. Mike Mullen, the new chairman of the Joint Chiefs of Staff, on Oct. 1, Mullen's first day on the job.

The Marines have been in Iraq's al-Anbar province, formerly one of the most violent places in the country but now considered an amazing turnaround.

According to The New York Times, which first broke the story, Marine units serving in Afghanistan would be able to command ground and air assault capability while the current Army forces there rely on the U.S. Air Force for air support.

Click here to read The New York Times story on Marine Corps redeployment.

FOX News' Mike Emanuel contributed to this report.