The U.S. military is likely to keep an expanded force of about 160,000 troops in Iraq (search) through the Dec. 15 election of a new government and then make a "fairly rapid" reduction to what has been the standard troop level of about 138,000, a senior Pentagon official said Thursday.

Marine Corps Lt. Gen. James T. Conway, the director of operations for the Joint Chiefs of Staff, told a Pentagon (search) news conference that there currently are "just short of" 160,000 American troops in Iraq.

"That's sort of the baseline figure that we think we'll probably see on through the election perio election, the 3rd Infantry Division will be leaving.

Conway also confirmed a Los Angeles Times report that the Pentagon is considering putting a general with more seniority in charge of a task force that has been struggling for two years to defeat the main weapon Iraqi insurgents are using to kill and maim American troops: the improved explosive device, or homemade bomb.

The task force, now headed by a one-star Army general, Joseph Votel (search), has been credited with finding various technological answers to the threat. But in the meantime the insurgents have managed to find new methods of devising and employing the weapon. Most U.S. troop deaths in Iraq in recent months have been caused by homemade bombs, even though U.S. forces find large numbers of them before they can be detonated.

Conway said the Pentagon may put a three-star general in charge of the task force, although no final decision has been made. He said the effort is getting maximum attention because "it's the only tool the enemy really has left in order to be able to take us on and cause casualties. And when we defeat that one method, it's over."

U.S. commanders have raised troop levels in advance of Iraqi elections because of expectations that the insurgents would intensify their attacks in an effort to stop the voting. Conway noted that after last January's election of an interim government, the U.S. military took about a month to reduce the size of its force from about 160,000 to the 138,000 level that prevailed for much of the rest of 2005.

Referring to plans for scaling back following the Dec. 15 election, he said, "I would say it would be fairly rapid," although potentially constrained by the availability of transport aircraft and ships to carry troops home.

"I think the answer is, as soon as possible, as soon as our logistics capability will allow us to do that, we will come back to that steady state" of about 138,000 troops, he said.

Some Democrats in Congress have been pressing the Pentagon to clarify a timeline for reducing troops levels in Iraq.

In a letter to Defense Secretary Donald H. Rumsfeld on Thursday, Sen. Barbara Boxer, D-Calif., said the uncertainty over when U.S. forces will be withdrawn from Iraq is untenable amid continued violence.

"I am writing to express my frustration over the administration's continued failure to set benchmarks for the drawdown of U.S. forces from Iraq and for the return of the National Guard," Boxer said. "As such, I request that you immediately make public to the American people what plan — if any — exists for a significant reduction in force levels after the upcoming elections in Iraq."

Appearing with Conway at the Pentagon news conference, Lawrence Di Rita, the chief spokesman for Rumsfeld, said decisions about future force levels would be made on the basis of recommendations by Gen. George Casey, the top U.S. commander in Iraq. Di Rita did not rule out that Casey may want even more troops after the election.

"General Casey could determine after the elections that, I want more, for whatever reason," Di Rita said, "and then he'll get more."