New throughout, adds details and background

By Valerie Volcovici and Trevor Hunnicutt

WASHINGTON, Feb 11 (Reuters) - President Donald Trump on Wednesday ordered the Defense Department to purchase electricity from coal-fired power plants in his latest effort to boost the coal sector.

The move, which was announced at the White House as an executive order, calls for the Pentagon to form purchase agreements to buy electricity from coal-fired power plants for an unspecified amount.

The president also announced that the Energy Department will provide six coal plants in Kentucky, North Carolina, Ohio, Virginia and West Virginia with $175 million for upgrades.

Utilities had been phasing out coal-fired generators, which are major sources of carbon emissions tied to climate change. Trump, who has called climate change a hoax, has promised to fast-track energy infrastructure to meet rising electricity demand from artificial intelligence and data centers.

Trump has declared an "energy emergency" to justify moves to keep open aging coal plants that have been set for closure and exempt aging coal plants from key air regulations. Trump has also removed tax incentives for wind and solar projects and his administration has slow-walked permits for renewable energy on federal land, as well as private and state lands.

On Thursday, Trump is set to undo the legal underpinning of most major greenhouse gas regulations at the Environmental Protection Agency called the endangerment finding. The EPA administrator has said this will be the biggest deregulatory action in U.S. history.

On Wednesday, Trump also announced that the Tennessee Valley Authority, the country's largest public utility, plans to delay the closure of two of its older coal-fired power plants in Tennessee.

(Reporting by Trevor Hunnicutt and Valerie Volcovici; Writing by Bhargav Acharya; Editing by Daphne Psaledakis, Caitlin Webber and David Gregorio)

((Bhargav.Acharya@thomsonreuters.com;))