A recent USA Today/CNN/Gallup Poll found that more than half of respondents want U.S. troops withdrawn from Iraq within the next 12 months.

Rep. John Murtha, D-Pa., a Vietnam War veteran who had been a staunch supporter of the Iraq War, has called for withdrawing troops as soon as possible.

So U.S. generals, Bush administration officials, lawmakers and even Iraqi leaders have started to clarify their thinking on how and when the 158,000 U.S. troops in Iraq should start to exit the country.

But for all the talk about exit plans, experts warn that a premature pullout would leave Iraq vulnerable to civil war and takeover by terrorists eager to export their violence.

''We have a national interest in Iraq that dwarfs where we were in Vietnam in the late 1960s,'' said professor Larry Diamond, a Stanford University political scientist who worked as a consultant for the Bush administration in Iraq.

Iraq's historic parliamentary elections Dec. 15 are likely to further intensify the debate. If the elections go well, as most of Iraq's political transition has, the pressure will increase to begin pulling the troops out.

Bush plan: Bush's mantra has been that U.S. troops will leave Iraq once its forces are strong enough to fight on their own.

Top administration officials have said troop reductions are in the offing.

Zalmay Khalilzad, the U.S. ambassador to Baghdad, recently told CNN that U.S. generals should be able to withdraw some forces early next year.

Secretary of State Condoleezza Rice was less specific but no less encouraging, telling Fox News, ''I do not think that American forces need to be there in the numbers they are now . . . for very much longer because Iraqis are stepping up.''

And, in a surprise move, Iraqi leaders meeting recently in Egypt advocated a timetable for U.S. withdrawal, although they were not specific about dates.

Iraqi forces are growing and gaining competence, according to an analysis by the nonpartisan Center for Strategic and International Studies. The number of Iraqi battalions able to take the lead in battle or fight without U.S. help has risen dramatically, from 11 in June to more than 35 in November.

Adm. Edmund Giambastiani Jr., vice chairman of the Joint Chiefs of Staff, said the Iraqi force has grown from 190,000 several weeks ago to 212,000.

Defense Secretary Donald Rumsfeld said that after the parliamentary elections he expects the U.S. troop level to drop from about 158,000 to 138,000, where it was for most of the year.

''Reductions beyond that are things the president will decide based on the recommendations from the battlefield commanders,'' he said.

And their thinking has started to change.

Generals' thinking: Bush's top generals in Iraq are growing increasingly concerned that their troops are fueling the insurgency simply by their presence, potentially marking a major change in the thinking about how many troops to keep in Iraq.

These generals have begun to acknowledge what war critics have been saying for months: that Iraq can only defeat the insurgency if it is able to resolve its own problems through a credible government.

''Increased coalition presence feeds the notion of occupancy,'' Gen. George Casey, lead American ground commander in Iraq, told lawmakers recently.

Casey has said he hopes to begin troop withdrawals in the spring if Iraq's political process remains on schedule and the nation's forces continue to improve.

Worried lawmakers: In a recent speech, possible presidential contender Sen. John McCain, R-Ariz., advocated adding 10,000 or more U.S. troops to Iraq, saying, ''We should be ramping up.''

But he is almost alone among his colleagues.

Senators from both parties, feeling growing public gloom over the war, are staking out exit positions.

Once an advocate of increasing troops, Democratic presidential hopeful Sen. Joseph Biden of Delaware recently said he expects 50,000 troops in Iraq to be redeployed by the end of 2006.

A bipartisan group of 79 senators passed a resolution telling Bush that 2006 needs to be ''a period of significant transition in Iraq.''

It wasn't the timeline some Democratic senators want. But the resolution said in bureaucratic language what Americans have been saying in polls, that U.S. troops need to start leaving Iraq at some point next year.