AUGUSTA, Maine — Debate over whether the state should fund a new study for an east-west highway across Maine devolved into a partisan battle on the Senate floor Tuesday before majority Republicans passed the bill.

Democrats, who united to vote against it, said they were not opposed to the concept of a feasibility study and were not opposed to the construction of a new toll road. What they were uncomfortable with was using public dollars to fund a study for what would be a privately financed project.

Republicans, however, said private investors already are lined up to fund this project, which many feel could be an economic boon for Maine. Those investors need assurance that the state is supportive before they can proceed, said Sen. Ronald Collins, R-Wells, co-chair of the Legislature’s Transportation Committee.

“Would you invest in something like this if the state wasn’t behind it?” he asked his colleagues.

The proposed “investor grade” study, to be conducted by an independent agency, is estimated to cost $300,000 and would come from the Maine Department of Transportation’s highway fund.

Democrats said the bill is not written in a way that limits funds.

“It’s a blank check. It just tells them to do the study,” said Sen. Bill Diamond, D-Windham. “Also, I think there is a feeling of ‘where did this money come from all of a sudden?’”

Other Democrats stood up to echo Diamond’s concerns about whether the state should buy into a private project.

Sen. Roger Katz, R-Augusta, said he couldn’t believe that a minor expense for such a major investment had turned into a partisan political issue.

“We will never spend $2 billion on this,” Katz said, referring to the estimated cost of an east-west highway. “But [$300,000] amounts to six one-thousandths of this project. That’s a pretty darn good deal.”

Sen. Elizabeth Schneider, D-Orono, spoke next.

“If it’s such a good deal, why aren’t we [the state] doing it?” she said.

Democrats proposed sending the bill back to the Transportation Committee to settle some of their concerns. One senator even suggested including the study in the highway fund bill.

In the end, the Senate voted 19-15 along strict party lines to pass the measure. It now goes to the House.

The idea for an east-west highway in Maine has been around for decades but movement has always stalled because no one wanted to build it.

During a public hearing last month, Cianbro Corp. Chairman Peter Vigue, a longtime proponent of an east-west highway, said he has been actively recruiting investors and has been talking to Canadian officials as well.

Vigue said the new corridor, paid for largely by tolls, would be a huge asset for companies — including his own firm — that move goods from Maine and Canada to the rest of the country. It would avoid communities but still be connected to communities, and would promote future growth by filling Maine’s “hollow middle.”

Sen. Doug Thomas, R-Ripley, the bill’s sponsor, made those same points Tuesday.

“This highway would make Detroit, Chicago, the west coast hundreds of miles closer to Maine,” he said.

The exact route of a proposed highway to connect New Brunswick to New Hampshire or Quebec would be part of the study.

Some environmentalists testified in opposition to the bill on the basis that it would increase pollution and lead to more burning of fossil fuels. Representatives of Maine’s railway transportation system also testified against the bill.