By Kristin Roberts

WASHINGTON (Reuters) - The Pentagon said on Monday it plans to send 39,000 soldiers to Iraq to replace troops scheduled to leave the war zone -- a move that could keep U.S. troop levels steady over the next year.

The United States has 155,000 troops in Iraq and is in the process of reducing that number to around 140,000 by mid-July, ending a "surge" of forces ordered by President George W. Bush last year to curb rampant violence.

While no decision has been made about future U.S. force levels, the deployment orders announced on Monday will ensure that commanders could keep 15 brigade combat teams plus support personnel there through fiscal 2009 if needed.

"All of these forces that we're talking about today are replacement forces," said Pentagon spokesman Bryan Whitman.

The troops will likely be sent to Iraq starting in October, the first month of the 2009 fiscal year.

Army Gen. David Petraeus, the top commander in Iraq, plans to assess security conditions after the current round of withdrawals is complete and could recommend further reductions.