WASHINGTON, Nov. 23 - The Pentagon is planning to make modest troop reductions after next month"s elections in Iraq and, if security conditions improve, could begin reductions next summer that would drop the American force level below 100,000 by late next year, Defense Department officials said Wednesday.

Troop reductions of this magnitude have been discussed by military commanders in the past, and it is not clear to what extent the most recent statements by various officials reflect the pressure on the Bush administration from Congress and even some Iraqi leaders to begin laying out withdrawal options. Officials said that no decisions had been made and that tentative plans for troop cuts could be abandoned if the insurgency gained strength or Iraqi security forces did not progress as quickly as their American trainers hoped.

"There is planning that is looking at, if the conditions are such that there could be reduction of the U.S. presence, how we could do that," said a Pentagon spokesman, Bryan Whitman. "We are also looking at contingency planning where you need to increase troop strength in Iraq."

In recent days, President Bush and his top advisers have all rejected calls to set a timetable for withdrawal, saying that to do so would embolden the insurgents. But they have talked, if only vaguely, about the possibility of reducing the numbers of troops. "I suspect that American forces are not going to be needed in the numbers that they are for that much longer," Secretary of State Condoleezza Rice said in an interview on CNN on Tuesday.

Mr. Whitman said that "the current thinking" is that the number of American troops, which is now over 150,000, would fall to around 138,000, where it was before a buildup to help provide security for the referendum on the constitution in October and the coming elections on Dec. 15 to choose a new government.

Officials have repeatedly emphasized that any decisions on troop reductions depend on whether security conditions worsen or whether Iraq"s new government demands quicker reductions. For at least the past year and a half officials have held out the prospect of troop reductions, but those reductions have not occurred.

A major decision point will be reached next spring, the officials said, after the new Iraqi government forms. Assuming security conditions allow it, the troop levels could drop by 20,000 to 30,000 more soldiers by then, the officials said.

A military officer in Iraq said Wednesday that the pace of the drawdown would be driven by how many Iraqi units were able to reach a readiness rating of level two, under the military"s scale of one to four. Level two means an Iraqi unit is capable of taking the lead on military operations but still needs American military support, as opposed to level one, in which an Iraqi unit can operate independently.

"The key is level two," the officer said. At that level, an Iraqi unit "will be able to control a local battle space just fine" as long as it receives continued American help with logistics, intelligence and transportation, he added. An increasing number of level-two Iraqi units in coming months will make it possible for a significant number of American combat troops to withdraw, he said, declining to specify how many.

Of the roughly 120 Iraqi Army battalions that are trained and conducting operations, roughly 40 are at level two, Lt. Gen. David H. Petraeus, who commanded the training effort in Iraq until earlier this year, said in a speech this month. The readiness of most police units, which some officials say are at least as important as the military in achieving stability, is still far below that of the Iraqi Army.

Senior Army officials remain concerned that pressure for withdrawals will drive officials in Washington to reduce the American troop levels before the Iraqis are ready to handle the primary role in fighting the insurgency. An Army official said that planners were discussing the option of keeping a brigade of 2,500 to 3,000 soldiers in Kuwait, so the unit could be rushed back to Iraq if security conditions worsened.

David E. Sanger contributed reportingfor this article.