PORTLAND — U.S. Sen. Susan Collins reiterated her support for a “gradual withdrawal” of American forces from Iraq rather than a fixed deadline for a pullout during a 28-minute speech Friday that championed bipartisanship as the solution to many of the nation’s seemingly intractable problems.

Speaking to a Rotary Club luncheon at the Portland Club, Collins said the nation “must chart a bipartisan course” in Iraq that will set the stage for “ a significant but responsible withdrawal of our combat troops and that crafts a lasting political solution to sectarian violence.”

If the United States “were to pack up and leave tomorrow,” Collin said, Iraq “would descend into genocide.” An early withdrawal would trigger “an expanded, broader civil war” and allow al-Qaeda to establish “a safe haven in Iraq,” she said.

Collins, who is seeking a third term in 2008, chided Democratic leaders in the Senate for blocking a vote on her plan to begin an immediate redeployment of American troops from a combat mission to other duties in Iraq, with the switch to be completed by next March. She says the mission of American forces should be redefined to focus on border security, training Iraqi forces and fighting terrorism, with an eye toward “a significant but responsible drawdown of our combat troops.”