WASHINGTON (CNN) -- Sen. Barack Obama, D-Illinois, said Wednesday he plans to introduce legislation to cap U.S. troop levels in Iraq, less than 30 minutes after his likely presidential rival Sen. Hillary Clinton, D-New York, announced she planned to introduce similar legislation.

"Escalation is a failed policy opposed by generals, Democrats and Republicans, and now even the Iraqis themselves, and the fact that the president is already moving ahead with this idea is a terrible consequence of the decision to give him the broad, open-ended authority to wage this war in 2002."

Obama, a member of the Senate since 2004, was not in the chamber to vote on the resolution authorizing the Iraq War in 2003. But he has voiced his opposition to the war from the very beginning.

Sens. Hillary Clinton, Joe Biden, Chris Dodd, John Kerry, and former Sen. John Edwards -- all potential rivals of Obama for the Democratic nomination -- voted in favor of the Iraq war resolution.