AUGUSTA — The Maine House gave initial approval Thursday to a bill that would require a comprehensive analysis of how Central Maine Power’s transmission line proposal would impact greenhouse gas emissions in New England and Canada.

But the future of the time-sensitive bill remains unclear. Supporters failed to garner the two-thirds majority that will ultimately be required to overturn a potential gubernatorial veto, much less affect the permitting process for the 145-mile high-voltage transmission line.

The bill, L.D. 640, would require an independent study of the regional impact on greenhouse gas emissions of the New England Clean Energy Connect project connecting Hydro-Quebec to the New England power grid.

Project opponents have questioned whether Hydro-Quebec will have to replace or supplement its hydropower with generation from non-renewable sources in order to supply Massachusetts ratepayers with the amount of “clean” electricity they plan to purchase.

“This is the normal type of modeling study that experts do in this type of business. In fact, it should have been done long ago,” said Rep. Ralph Tucker, D-Brunswick. “We need to verify that the project will result in net reductions of greenhouse gas (emissions) overall and not just in New England.”

The bill would require the study to be completed by mid-August, before the Maine Department of Environmental Protection and the Land Use Planning Commission decide on CMP’s permit applications. The Maine Public Utilities Commission already has granted the project a key certificate to move forward.

But to meet that tight timeline, the study would need to begin very soon. And that would require two-thirds votes in both the House and Senate to pass the bill as an “emergency measure” effective immediately and to overturn a potential veto from Gov. Janet Mills, who supports the project.

The initial 74-64 vote moves the bill forward but is well short of the two-thirds majority that would be needed on final passage. A subsequent 87-50 vote on an amended bill – requiring a Maine PUC program to fund the study, rather than private groups – fared slightly better but was still shy of the two-thirds mark.

Opponents portrayed the bill as another wasted effort that may not yield objective results, especially if project opponents and interest groups are allowed to pay for the study.

“I suggest that we do not need another study and that the time is now to act on climate change,” said Rep. Lois Galgay Reckitt, D-South Portland. “I don’t like CMP any more than the rest of you. But I will not let my personal feelings affect my vote when we have an opportunity to take meaningful action to address climate change.”

The bill now heads to the Maine Senate for consideration and faces additional votes in the House.