When Republican Jim DeMint of South Carolina in January offered an amendment to a Senate ethics bill that would have broadened earmark disclosure rules, Majority Whip Richard J. Durbin moved to kill the proposal.

Seven Republicans sided with Durbin, D-Ill. Still, Democratic leaders lost the vote, 46-51, thanks in part to two freshmen in their caucus — Jon Tester of Montana and Jim Webb of Virginia — who along with seven other Democrats voted against the motion to table the amendment.

The new earmark language became part of the bill (S 1), and the defections gave Senate Democratic leaders a preview of the independent streak in the party’s freshman class.

So far, the voting records of three Democrats who unseated conservative Republican senators in Republican-leaning states last fall have set them apart from the rest of the Senate Democratic Caucus. While other Democratic freshmen have voted with a majority of the members of their party more than 95 percent of the time, Webb, Tester and Claire McCaskill of Missouri more often have gone their own way, mainly on budget and ethics issues.

According to a Congressional Quarterly analysis, Tester and Webb have voted with a majority of Democrats about 90 percent of the time. McCaskill has voted in line with a majority of her party on about 87 percent of the Senate’s roll call votes on which a majority of Democrats are aligned against a majority of Republicans.

The only Senate Democrats with lower party unity scores are Ben Nelson of Nebraska, Mary L. Landrieu of Louisiana and Evan Bayh of Indiana, all of whom cultivate moderate images while representing Republican-leaning states.

McCaskill said Nelson is one of the Senate veterans she talks to on a regular basis.

“As a freshman there are a lot of pressures, but she’s looking at the people in her party who remain independent,” said McCaskill spokeswoman Adrianne Marsh.

McCaskill was one of four Democrats who voted on March 23 for an amendment to the Senate version of the fiscal 2008 budget resolution (S Con Res 21) that would create a 60-vote hurdle in the Senate for appropriations bills that would spend additional money without setting aside an equivalent amount for debt reduction.

Tester was among 21 Democratic senators, including four freshmen, who voted for Nelson’s unsuccessful budget amendment calling for a reduction in the estate tax. “It’s a big issue — one we heard about in the field,” Tester said. “I’m going to vote for what Montanans need. I don’t consult with Democrats on all these votes.”

Both Tester and McCaskill backed a successful Republican amendment on March 21 that would create a 60-vote threshold for legislation that would increase income tax rates.

Webb — whose state is home to Philip Morris USA, the world’s largest cigarette maker — was one of four Democrats on March 23 who opposed a non-binding amendment to the budget that called for a cigarette tax increase to provide more money for the State Children’s Health Insurance Program. Webb said a cigarette tax would hurt the poor.

Four other Democratic freshmen — Benjamin L. Cardin of Maryland, Sheldon Whitehouse of Rhode Island, Amy Klobuchar of Minnesota and Sherrod Brown of Ohio — came to the Senate with more traditional Democratic credentials. They have all voted with a majority of their party more than 95 percent of the time, as has Bob Casey of Pennsylvania, who is a party renegade on abortion-related issues and gun control.

In addition to backing DeMint on the ethics bill, Tester supported an amendment to that bill by Louisiana Republican David Vitter that would have barred members of Congress from paying their families for campaign work.

McCaskill supported a proposal strongly opposed by Majority Leader Harry Reid, D-Nev., that would have created an independent Office of Public Integrity.

Also, McCaskill is carving out a niche for herself as budget hawk. In addition to backing the 60-vote hurdle for income tax rate hikes, she was the only Democrat to support an unsuccessful DeMint amendment to the budget resolution calling for legislation that would prevent Congress from using Social Security tax revenue for other purposes.

While Tester’s voting record so far is more conservative than that of most in his caucus, Montana Democrats insist that he cannot be pigeonholed ideologically.

“I resent the term ‘moderate.’ He’s a populist connected to the pulse of the state,” said Jim Farrell, executive director of the Montana Democratic Party. President Bush and Vice President Cheney “are as unpopular in Montana as they are in the rest of the country . . . and Tester votes the way Montanans would” on issues of taxes and war.

And Webb does not want to be pegged as “fiscally conservative,” either.

“People thought he would be a closet Republican, and that’s been entirely false,” said Webb spokeswoman Jessica Smith. “He doesn’t believe anyone should be in lock step with their party. . . . He isn’t fiscally conservative but more of a strong believer in fiscal accountability.”

None of the Senate’s eight freshmen have voted with Republicans on any close war-related votes. And the Senate freshmen are sensitive about backing Reid on parliamentary issues, such as cloture votes.

McCaskill said Reid has approached her a few times to make sure she is on board with Democrats on process issues. “He said they hope to have full support on procedural votes, at least,” McCaskill said.

But Tester, a former president of the Montana Senate, said although he is sensitive to the need for party unity on procedural votes, his constituents come first. “If Harry were to call and say, ‘I really need you on this,’ I’m still going to vote with what Montanans need,” said Tester.

Daphne Retter and Greg Giroux contributed to this story.