CONCORD, N.H. — The U.S. Department of Energy plans to reveal details of possible alternative routes for the Northern Pass electrical transmission project before it releases a draft environmental study on the proposal, likely by the end of this year, according to a letter sent to the state’s congressional delegation.

In a letter released Wednesday by the delegation, the department said it is reviewing more than 7,500 public comments as it considers a permit application for the $1.4 billion Northern Pass.

The delegation had twice asked for details of all alternatives to be released and Northern Pass Transmissions, the project sponsor, also wanted the alternative routes revealed.

The project would run 187 miles of transmission lines carrying 1,200 megawatts of electricity — enough to power 1.2 million homes — from Canada to the southeast part of the state. Backers point to clean renewable power and job creation while opponents say it would harm the state’s natural beauty.

U.S. Sens. Kelly Ayotte and Jeanne Shaheen and Reps. Annie Kuster and Carol Shea-Porter asked DOE in August and again last month to see details of the alternative routes. The four pressed DOE to keep the review process as open as possible, given the strong feelings it has stirred on both sides.

“DOE’s commitment to issue a public preliminary report on alternatives is a positive step forward that will improve transparency for New Hampshire citizens,” the delegation said in a joint statement. “We look forward to working with DOE to make sure Granite Staters have the opportunity to thoroughly review and comment on the alternative routes prior to the issuance of the draft Environmental Impact Study.”

As part of the process considering whether to issue a presidential permit allowing Northern Pass to proceed, DOE works with other federal agencies and the state to determine what effects the project could have on the environment. In the letter to the delegation dated Monday, it said it expects to issue a report in March that summarizes all the information it received during a public comment period.

Following that March report, it will release the details of alternative routes reviewed before it finishes a draft Environmental Impact Statement in late 2014.

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