The agreement went into effect Jan. 1, and it calls for U.S. combat troops to be out of Iraqi cities and towns by the end of June and out of Iraq by the end of 2011.
"It balances the interests of both countries as we see the emergence of a sovereign Iraq in full control of its territory," Gates said. Iraq's provincial elections, to be held Jan. 31, are another sign of progress, he added.
The agreement marks an important step forward in the orderly drawdown of the American presence, the secretary said. "It is a watershed, a firm indication that American military involvement in Iraq is winding down," he said. "Even so, I would offer a few words of caution."
Violence is low, Gates told the House members, but the potential exists for setbacks. "And there may be hard days ahead for our troops," he told the representatives.
Even with the military drawdown, Gates said, he expects American presence will still be felt in Iraq.
"We should still expect to be involved in Iraq, on some level, for many years to come, assuming a sovereign Iraq continues to seek our partnership," Gates said. This would be in an advisory and assistance mode negotiated between two sovereign nations, he said.
The secretary said President Barack Obama is committed to a responsible and safe drawdown of troops in the country. The president will hear from Multinational Force Iraq cCommander Army Gen. Raymond T. Odierno, U.S. Central Command chief Army Gen. David Petraeus and the members of the Joint Chiefs of Staff. In fact, Gates said, the president will meet with military leaders at the Pentagon tomorrow.
Gates said that he and Navy Adm. Mike Mullen, the chairman of the Joint Chiefs of Staff, will continue to have regular conversations with the president.
"We are laying out - with each of the options we will present to him - each of the commanders' views of the risks that are associated with that timeline," Gates said. "So I think that he has entirely asked for a range of options - including the 16-month - and we will give him that. He has asked for some of our assumptions and for more analysis in certain areas, and I think this is a very thorough and real process. I don't think anybody associated with it in the Department of Defense thinks we are going through the motions, that a decision has already been made."
Though the military's focus is shifting from Iraq to Afghanistan, Gates said, Iraq remains crucial to the stability of the Middle East.