By Kristin Roberts

WASHINGTON, Dec 21 (Reuters) - The United States should be able to withdraw five combat brigades from Iraq by mid-2008 because troops have held onto security gains made this year, U.S. Defense Secretary Robert Gates said on Friday.

The planned withdrawals from 20 combat brigades was announced in September based on a recommendation from the U.S. commander in Iraq, Gen. David Petraeus. But withdrawals were dependent on U.S. forces' ability to maintain improved security.

"The situation on the ground, I think, makes it likely that Gen. Petraeus will be able to decide and bring out the first five (brigade combat teams) by July, as he indicated in September," Gates told reporters.

The first of those brigades leaves Iraq this month.

The Pentagon boosted Iraq troop levels by about 30,000 this year as part of a security crackdown that reduced violence throughout the country.

The United States now has about 158,000 troops in Iraq. Under the current plan, the Pentagon would pull five brigades out by July, reducing the force by about 20,000 combat troops plus support personnel.

Gates has said he would like to see another five brigades taken out of Iraq in the second half of 2008 as well.

That would leave about 10 combat brigades, or about 100,000 U.S. troops, in Iraq by the end of the Bush administration.

"It'll be completely dependent on the circumstances on the ground," Gate said. "We obviously want to sustain the gains that we have already made."

Military commanders provide their next major assessment of the Iraq war, including an assessment of future troop reductions, in March.

"All of this is conditions-based and it will depend very much on the analysis and recommendations that the senior military commanders and advisors to the president make in March," Gates said in his last press briefing of the year. (Editing by Bill Trott)

AlertNet news is provided by