WASHINGTON — The Trump administration on Monday moved to weaken an Obama-era regulation aimed at limiting the seepage of toxic pollution into water supplies from the ash of coal burning power plants, a change that coal industry leaders say could keep plants open longer and which environmental groups fear will increase the risk of water contamination.

Andrew Wheeler, the administrator of the Environmental Protection Agency, issued the proposed regulation, which relaxes rules set in 2015 imposing stringent inspection and monitoring rules at coal plants and requiring plants to install new technology to protect water supplies from arsenic, lead, selenium and other toxic effluent.

The rules are part of President Trump’s vast environmental deregulation agenda aimed largely at eliminating rules the fossil fuel industry finds burdensome and extending the life of coal burning power plants. In addition to discharging pollutants into the air and water, coal plants are the top source of United States carbon dioxide emissions, the principal greenhouse gas warming the planet.

The new measures lower pollution limits, extend the deadline for power plants to comply with new technologies until Dec. 31, 2028, and exempt many coal plants altogether.

Want climate news in your inbox? Sign up here for Climate Fwd:, our email newsletter.