Senate appropriators pressed President Trump on Thursday to ensure adequate funding for the Department of Energy after a draft White House budget showed it would gut the agency's renewable office by 70 percent, along with steep cuts to its nuclear and fossil programs.

"Government-sponsored research is one of the most important investments our country can make to encourage innovation, unleash our free-enterprise system to create good-paying jobs and ensure American competitiveness in a global economy," the senators, led by Republican Sen. Lamar Alexander of Tennessee, wrote in a letter to the president.

Alexander is chairman of the Senate Appropriations Committee's panel on energy that reviews the Energy Department's budget. A number of other top Republicans signed the letter, including Sens. Lisa Murkowski of Alaska, Susan Collins of Maine, Lindsey Graham of South Carolina and all other appropriators.

Trump is expected to release his fiscal 2018 budget proposal next week. It will go to Congress, where it will be reviewed and likely modified if lawmakers disagree with the president's priorities.

"We cannot lose the technological advantages we have gained through our country's investment in research and development," the senators wrote. "Governing is about setting priorities, and the federal debt is not the result of Congress overspending on science and energy research each year. We urge you to continue to invest in the Department of Energy's research and development programs in fiscal year 2018."

The letter did not specify how much funding the Energy Department should receive.

The renewable office's appropriated funds would plummet from $762 million for fiscal 2017 to $160 million under Trump's fiscal 2018 proposal, according to the draft obtained by Axios. The draft also would cut the fossil energy office by 54 percent and the nuclear programs by 31 percent.

The draft was released after Senate Democrats prodded Energy Secretary Rick Perry on Tuesday over reports that he is denying clean energy and other funding to academic researchers, arguing that such a freeze under the current fiscal 2017 budget would be unlawful.