A new survey commissioned by the Afghanistan Study Group reveals that conservatives and tea party voters are growing concerned about the sustainability of US operations in Afghanistan.

Sixty-six percent of conservatives said the US should diminish its military presence in Afghanistan -- 39 percent supported reduced troop levels while 27 percent championed prompt withdrawal.

Conservatives narrowly believed the war was worth fighting, by a margin of 46 to 39 percent. But a large majority of them were concerned about its high costs, and over half believed troop levels could be reduced without compromising US security.

The study (.PDF), conducted by the Virginia-based Third Eye Strategies between Jan. 4-10, surveyed 1,000 registered voters across age groups who self-identify as conservative. Five-hundred and fifty of them said they support the tea party movement.

Of tea party supporters, the epicenter of the Republican base, a mere 28 percent thought the US should continue on its current course, as 64 percent insisted the government ought to either reduce troop levels (37 percent) or begin withdrawing from the region (27 percent).

The survey casts a harsh light on an ongoing war that conservative lawmakers have largely pronounced as vital to American interests. Its high price tag and lack of a time-table seem to be provoking second thoughts among a group of voters who say they're highly concerned about the national debt.

If the trend continues, it could prove a critical turning point for a military effort that the Obama and Bush administrations have unequivocally championed. A CNN/Opinion Research Corporation poll last week found that 63 percent of Americans oppose the war, while only 35 percent said they support it.

Military operations in Afghanistan are slated to cost $119 billion in the fiscal year 2011, according to the Congressional Research Service (.PDF), having risen dramatically in recent years.

High-profile conservative tax activist Grover Norquist on Tuesday urged the right to thoughtfully consider the costs and viability of the war, questioning whether it truly advances US interests, Dan Froomkin reported at the Huffington Post.

Liberals oppose the war in much larger percentages, worrying about the costs and the possibility that US efforts are fueling extremism in the region and bolstering a corrupt government.

The Afghanistan Study group, founded by Steve Clemons and Richard Vague, defines itself as a "bipartisan ad hoc group of public policy practitioners, former U.S. government officials, academics, business representatives, policy-concerned activists and association leaders concerned with the Obama administration’s policy course in Afghanistan."

Its survey results had a 4.2 percent margin of error.