WASHINGTON – The Bush administration planned to issue the nation’s first regulations to cut mercury pollution from electric utilities Tuesday, relying on a market trading system that gives companies 15 years to reduce it nearly by half.

The Environmental Protection Agency’s regulations are aimed at reducing levels of a toxic chemical that can severely damage nervous systems, especially in fetuses and children. They result from a lawsuit brought by an environmental group 13 years ago.

The EPA expects to reduce the current 48 tons a year of mercury from smokestacks of coal-burning power plants down to 31.3 tons in 2010, according to a copy of the rule provided Monday by environmental groups. The regulation would further reduce that to 27.9 tons in 2015, and to 24.3 tons in 2020.

Maine Sen. Olympia Snowe said in a press release that the new mercury emissions rule “is woefully inadequate,” adding that the system does not reduce overall emissions to acceptable levels until 2018.