One of the state’s leading environmental groups released its scorecard Thursday for the 126th Legislature, setting the stage for a flood of political advertising to support favored candidates or unseat those who failed to make the grade.

The Maine League of Conservation Voters has issued “grades” since 1986. Over that time the organization and its political action committee have used the report cards in conjunction with advertising designed to hold lawmakers accountable for their voting records on environmental bills and influence outcomes in legislative elections.

The group spent about $50,000 on such advertising in 2012 and about $338,000 in 2010, and this week launched a $400,000 television ad campaign contrasting the environmental records of Republican Gov. Paul LePage and his Democratic challenger, U.S. Rep. Mike Michaud.

Beth Ahearn, the group’s political director, said the organization had not decided which legislative races it would be involved in this year. Ahearn said the league’s advertising and election-communication budget would be similar to previous years.

The grades issued Thursday were based on 13 bills that lawmakers considered in 2012 and 2013. The proposals included creating a 25-foot setback from lakes for fertilizer application; including water protections in Maine’s metal-mining rules; requiring manufacturers to disclose use of the chemical BPA in food packaging; promoting so-called food hubs to distribute local food to schools and hospitals; reopening the St. Croix River to alewives; authorizing a comprehensive study of the effects of climate change in Maine; and reinstating rebates for solar power users.

Twelve of the 13 bills received initial approval by the Legislature. Six were vetoed by LePage, and the Legislature ultimately failed to override the six vetoes. In some instances, lawmakers reversed their early support to help uphold LePage’s veto.

The food hubs bill was an example. The measure passed the Senate 33-0 and the House 120-19, but was ultimately defeated after Republican lawmakers changed their votes to uphold LePage’s veto.

“It is an unfortunate setback for Maine that all the hard work to pass the food hubs bill was undone by politics,” said Sen. Chris Johnson, D-Somerville, the bill’s sponsor.

The grades were favorable for most Democrats. Fifty-eight of the 88 Democrats in the House of Representatives received a score of 100 percent, while another 15 received a score of 92 percent to make the group’s “honor roll.” In the Senate, 17 of 19 Democrats made the honor roll and 14 scored 100 percent.

Sen. Rebecca Millett, D-South Portland, received a score of 83 percent, as did Sen. Troy Jackson, the Democratic majority leader from Allagash. Millett may have received a higher grade, but was absent for several of the votes. Jackson, on the other hand, was docked for votes opposing the alewives and metal mining bills. Jackson, who lost to Sen. Emily Cain, D-Orono, in the June primary for the 2nd Congressional District, was targeted by the League of Conservation Voters, the parent organization of the Maine chapter.

Overall, the lowest score for Democrats in either chamber was 54 percent by Rep. Matt Peterson of Rumford, who was docked for missing votes while he was out with a medical condition.

Conversely, the highest-scoring Republican was Don Marean of Hollis. He received an 85 percent rating for supporting 11 of the 13 bills.

“I am a Teddy Roosevelt Republican,” Marean said in a statement. “This session I voted to protect our natural resources, to encourage clean renewable power, and to encourage wider distribution of local foods. I believe that a strong economy depends upon good stewardship of our land, air and water.”

Marean was in rare territory for Republicans and the only one to break the 80 percent threshold. Of the 58 Republicans in the House, only 12 received a score of 50 percent or higher. In the Senate, only four received a score of 50 percent or higher.

The group named five Republican lawmakers to its “dishonor roll”: Reps. Dale Crafts of Lisbon, Jeffrey Gifford of Lincoln, David Johnson of Eddington, Ricky Long of Sherman and Sen. Doug Thomas of Ripley. Each received a score of 8 percent. Johnson was absent much of the session because of an illness.

While the lawmakers on the “dishonor roll” would seem likely targets in the election, the Maine League of Conservation Voters has often steered clear of spending resources on Republican lawmakers in safely conservative legislative districts. Instead, it has sometimes focused on key votes by Republican lawmakers in swing districts.