EPA Administrator Scott Pruitt testifies before the House Appropriations Committee Subcommittee on Interior, Environment, and Related Agencies Subcommittee on Capitol Hill in Washington Thomson Reuters WASHINGTON (Reuters) - U.S. Environmental Protection Agency chief Scott Pruitt will testify in front of a Senate subcommittee on Wednesday about his agency's budget, exposing him to fresh questions about his travel and security spending.

Pruitt has been under pressure from mainly Democratic lawmakers in recent weeks over a series of controversies ranging from his use of first-class travel to his 24/7 security detail and costly office renovations - but has retained the support of President Donald Trump and most Republicans for his efforts at EPA to roll back regulations characterized as obstacles to industry.

Pruitt is scheduled to appear before the 13-member Senate Appropriations Committee's subcommittee on Interior, Environment and Related Agencies on Wednesday morning regarding the EPA's 2019 budget - which Trump has proposed to cut by a fourth.

Most of the committee's six Democratic members have been vocal oponents of Pruitt's regulatory rollbacks at EPA and have criticized him for alleged ethical missteps while in office related to his spending and his lease of a room in a Washington condo linked to an energy lobbyist.

The controversies have triggered 12 investigations by the EPA's inspector general, congressional committees and the White House.

Several Democrats on the subcommittee, including Senator Diane Feinstein and Senator Patrick Leahy, have called for Pruitt's resignation.

He has also faced growing pressure from some Republican senators not on the panel over his handling of U.S. biofuels policy.

Senator Chuck Grassley of Iowa, for example, said on Tuesday he would join the chorus of lawmakers calling for Pruitt's ouster unless the EPA chief rolls back the agency's use of waivers exempting refineries from their obligation to mix ethanol into fuel.

Separately, the House Energy and Commerce Committee is scheduled to interview EPA Assistant Administrator Bill Wehrum on Wednesday morning about efforts to ease air pollution permitting for power plants and industrial facilities.

Wehrum, whose office also runs the biofuels program, is likely to have to field questions about the EPA's handling of biofuels regulations - including the administration's proposals to tweak them in a way that reduces costs for refiners.

(Writing by Richard Valdmanis; editing by Jonathan Oatis)