In a move that disappointed environmentalists who usually support him, Maryland Gov. Martin O’Malley announced Tuesday that he plans to sign legislation that will put incineration of garbage on par with solar and wind power as a source of renewable energy.

In a statement, O’Malley (D) said that after “careful deliberation,” he concluded that a bill passed last month would help Maryland reach an “aggressive goal” of generating 20 percent of its energy from Tier I renewable energy sources by 2022.

“It is only through a diverse, renewable fuel mix that we will be able to reach our aggressive goals, protect our precious environment and create the economic engine to move Maryland forward,” O’Malley said.

Maryland, 28 other states and the District have renewable energy standards. Over the next decade, state law requires power companies to get more of their energy from renewable resources.

Under current law, electricity from waste incineration is classified as a second-tier source. The bill sent to O’Malley would elevate its status — which opponents say is a boon to a small number of waste-to-energy plants and does little to help the environment.

“We are disappointed in the governor’s decision,” said Jen Brock-Cancellieri, deputy director of the Maryland League of Conservation Voters. “Coming off the recent elections, we heard loud and clear that voters want to invest in a clean-energy economy, and we don’t believe incineration plays a part in that.”

Brock-Cancellieri called the bill “a bad deal for consumers, a bad deal for the environment and the wrong way to move Maryland forward.”

Debate over the bill put O’Malley in a difficult spot. Many of the groups opposed to the bill stood side by side with the governor as he pressed unsuccessfully for legislation to spur the development of offshore wind power and limit construction of septic systems.

Maryland’s energy administration backed the incineration bill, and so did the government in Montgomery County — the only local jurisdiction in Maryland that controls a waste-to-energy plant that is certified as a renewable source. But the bill was opposed by seven of Montgomery’s eight state senators.