The Obama administration has decided to drop the number of U.S. troops in Iraq at the end of the year down to 3,000, marking a major downgrade in force strength, multiple sources familiar with the inner workings and decisions on U.S. troop movements in Iraq told Fox News.

Senior commanders are said to be livid at the decision, which has already been signed off by Defense Secretary Leon Panetta.

Panetta, touring sites Tuesday in advance of the Sept. 11 10th commemoration, insisted "no decision has been made" on the number of troops to stay in Iraq.

"That obviously will be the subject of negotiations with the Iraqis and as a result of those negotiations. As I said no decision has been made of what the number will be," he said.

Currently, about 45,000 U.S. troops are stationed in Iraq. The generals on the ground had requested a reduced number of troops remaining in Iraq at the end of the year, but there was major pushback about "the cost and the political optics" of keeping that many in Iraq. The military's troop-level request was then reduced to 10,000.

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Commanders said they could possibly make that work "in extremis," in other words, meaning they would be pushing it to make that number work security-wise and manpower-wise.

Now, sources confirm that the administration has pushed the Pentagon to cut the number even lower, and commanders are concerned for the safety of the U.S. troops who would remain there.

"We can't secure everybody with only 3,000 on the ground nor can we do what we need to with the Iraqis," one source said. Another source said the actual total could be as high as 5,000 when additional support personnel are included.

A senior military official said by reducing the number of troops to 3,000, the White House has effectively reduced the mission to training only.

"There is almost no room for security operations in that number; it will be almost purely a training mission," this official said. The official added that a very small number of troops within that 3,000 will be dedicated to counter-terrorism efforts, but that's not nearly what Gen. Lloyd Austin, the top U.S. commander in Iraq, wanted.

This shift is seen by various people as a cost-saving measure and a political measure. White House spokesman Jay Carney said Tuesday that the U.S. has operated responsibly to meet the year-end deadline to remove troops from Iraq, per a 2008 Status of Forces Agreement.

He added that negotiations with the Iraqis will determine the outcome, and while costs are a factor in every decision, the administration makes decisions on what is best for the United States.

The only administration official fighting for at least 10,000 forces to stay in Iraq at the end of the year was Secretary of State Hillary Clinton, sources said. But she has lost the battle.

Responding to the news, Sen. Joe Lieberman, D-Conn., who has traveled to Iraq many times, said that in all the conversations he has had on force strength, he has "never heard a number as low as 3,000 troops to secure the gains Iraqis have won over the years."

Lieberman said his first question for the administration is whether the number is one Iraqis had requested or if it was chosen according to other criteria.

Sen. Lindsey Graham, R-S.C., said reducing the troop presence to 3,000 "would put at risk all the United States has fought for in Iraq."

"The biggest winner of a U.S. decision to move to 3,000 troops in Iraq would the Iranian regime. The ayatollahs would rejoice," he said.

Any of the plans will require Iraqi approval, and on that front, the Pentagon recently secured a commitment from the Iraqis to start negotiations, but they have not agreed to any number.

"Discussions with the Iraqis on our post-2011 strategic relationship are ongoing, and no decisions on troop levels have been made," said Panetta spokesman George Little. "We continue to proceed with troop withdrawals as directed by the president."

On Tuesday, the head of the three-province Kurdish autonomous region in the north of Iraq, warned that if American troops leave sectarian violence might resurface. Massoud Barzani urged the central Iraqi government to sign an agreement with the U.S. to keep forces in the country.

Fox News' Bret Baier contributed to this report.