The report was released two days before top commander Gen. David Petraeus and Ambassador Ryan Crocker brief Congress on the situation in Iraq and prospects for American troop reductions. Their recommendations, which President Bush has signaled he will accept, could largely determine the course of action in Iraq for the coming year.
The report cited security improvements in Iraq since the buildup of U.S. forces in 2007, but credited factors outside U.S. control, such as help from mostly Sunni fighters who turned against al-Qaida and a truce by a Shiite militia.
"The U.S. is no closer to being able to leave Iraq than it was a year ago," it concluded. "Lasting political development could take five to 10 years of full, unconditional U.S. commitment to Iraq."
The U.S. Embassy in Baghdad did not immediately respond to an e-mailed request for comment. But U.S. officials have repeatedly said that some political goals have been achieved in Iraq thanks in part to the buildup of forces, though they acknowledge that much remains to be done.
The institute's report warned that a substantial reduction of U.S. troops in Iraq risks "a complete failure of the Iraqi state, massive chaos and even genocide."
If the Americans opt for a reduced commitment, the report said, they should focus on improving political and economic development.
But an unconditional withdrawal of U.S. troops from Iraq must be coupled with an increased American military presence in neighboring countries, ready to intervene in case of a major crisis in Iraq, the report said. The U.S. should also redouble efforts to build regional political alliances, it added.
In the past year, Iraq's parliament has passed legislation the U.S. considers key to the country's future stability, including relaxing a ban on former Saddam Hussein supporters in government, an amnesty for some prisoners, increased powers at the provincial level and approval of a national budget.
But implementation of those policies has been uneven, the report said.
"Without political progress, the U.S. risks getting bogged down in Iraq for a long time to come," it concluded.