Washington ? The Bush administration has for now ruled out creating a timetable for withdrawing U.S. troops from Iraq after Sunday’s elections, but military commanders have charted a plan to have Iraqi security forces begin taking the lead in combat operations in certain parts of the country as early as spring.

U.S. officials have identified areas in southern and northern Iraq that have remained relatively free of violence as the best candidates for a piecemeal shift in military responsibilities over the months ahead. Under this approach, as Iraqi forces take on more of the counterinsurgency mission, some U.S. troops would assume an emergency backup role or shift to training Iraqi units, and others might leave the country, according to administration officials and others familiar with the plan.

Under optimal conditions, commanders anticipate possibly being able to withdraw, sometime this spring or summer, three of 20 brigades in Iraq, or about 15,000 troops. That would lower the level of U.S. forces in Iraq to where it was before it was raised to 150,000 troops last month.

More reductions, however, are considered unlikely until the end of 2005 or early 2006. Officials said they would look at establishing a phased pullout predicated on achieving certain benchmarks, basing it on conditions on the ground rather than dates on a calendar.

The question of U.S. withdrawal has become especially acute in Washington in the days leading up to today’s elections, which will open a new phase in the U.S. involvement in Iraq. White House officials worry that Americans will see the vote as a natural turning point and expect quick reductions in U.S. forces afterward. In the face of growing pressure in Congress to begin bringing troops home, President Bush has tried to prepare the public for a long-term deployment.

“As democracy takes hold in Iraq, America’s mission there will continue,” Bush said in his weekly radio address Saturday. “Our military forces, diplomats and civilian personnel will help the newly elected government of Iraq establish security and train Iraqi military police and other forces. Terrorist violence will not end with the election. Yet the terrorists will fail, because the Iraqi people reject their ideology of murder.”

Sen. Edward Kennedy, D-Mass., last week called on Bush to begin withdrawing U.S. troops “immediately,” with a complete pullout by early next year. Other Democrats have begun voicing similar proposals. So far, congressional Republicans remain solidly behind the president but privately fret that the administration has no exit strategy and that the political heat for a timetable will reach a boiling point.

Despite the pressure, the administration wants to avoid setting any deadlines for withdrawals, officials said. They said they were mindful of the experiences of President Clinton, who repeatedly set and broke deadlines for withdrawing peacekeeping troops from Bosnia in the 1990s.

Predictions of how quickly U.S. troops can train a new set of Iraqi security forces and defeat the insurgency have proven overly optimistic, officials acknowledged. And the shape of the new interim government that will emerge from today’s elections has added a wild card to forecasts.

There are also political considerations. “When you put yourself in the position of setting dates, you then get criticized politically for missing them and that can give the enemy a propaganda advantage,” said a senior administration official who, like others interviewed for this article, spoke on the condition of anonymity because the issues are politically and diplomatically sensitive.