A new proposal backed by the Senate majority leader, Harry Reid of Nevada, to cut off funding for the Iraq war is creating another thorny political test for Senator Clinton as she tries to adopt a position on the plan that will appeal both to primary and general election voters.

The proposal, which would cut off funding for American combat forces in Iraq by March 31, 2008, has almost no chance of passing in the Senate, but it could be used by anti-war voters to judge the pack of Democratic presidential hopefuls.

During a campaign stop yesterday in the first presidential caucus state, Iowa, Mrs. Clinton said she has not yet decided where she stands on the measure.

According to the Associated Press, she said Congress first should pressure President Bush to agree to the funding bills it has already passed, which set a nonbinding target of withdrawing troops from Iraq.

“I’m looking at that,” she said of the new proposal backed by Mr. Reid. “I don’t know anything about it.”

In the past, Mrs. Clinton has said that while she supports cutting funding for Iraqi troops, she does not favor such cuts for American forces.

Remaining silent on the new proposal for much longer, however, is going to be difficult for the former first lady.

During campaign stops around the country, Mrs. Clinton regularly fields questions about her position on Iraq. And if the proposal reaches the Senate floor, she will have no choice but to take a position on it — a move that will be tricky for her as she tries to stave off the strong anti-war challenge of her two major rivals for the Democratic nomination, Senator Obama of Illinois and John Edwards.

Yesterday, another Democratic presidential contender, Senator Dodd of Connecticut, announced his support for the proposal.

Senator Feingold, a Democrat of Wisconsin, is expected to introduce it next week if Mr. Bush vetoes the nonbinding legislation passed earlier by Congress, as he has promised.

Mr. Bush said yesterday that any legislation containing a troop withdrawal date or a cut to funding would have a boomerang effect.

“The bottom line is this: Congress’s failure to fund our troops on the front lines will mean that some of our military families could wait longer for their loved ones to return from the front lines,” he said.

A Democratic blogger, Bob Geiger, called the proposal a “gut check” for Democrats because unlike the nonbinding war measure, this one would have the teeth of Congress’s purse strings.

Supporting the new proposal is risky move for many moderate Democrats, who will have to face voters who think a funding cut is unwise.

Mr. Edwards, a former senator of North Carolina, is already on the record as supporting a funding cut. Mr. Obama’s campaign did not return calls for comment yesterday. But many political analysts are looking to what Mrs. Clinton will do.

“She’s the one that’s tried to reserve the option for the general election of appearing more moderate,” a professor of political science at the University of Virginia, Larry Sabato, said. “It’s going to be tougher for her to appear moderate if she endorses this,” he added. “On the other hand, if she doesn’t endorse it, the odds are most of her opponents are going to endorse it.”