WASHINGTON — The White House is moving to propose slashing cuts to longtime Republican targets like the Environmental Protection Agency in a set of marching orders to agencies as it prepares its budget for the upcoming fiscal year.

Capitol Hill aides say the White House budget office will send proposed levels for the 2018 budget year to agencies Monday. The aides spoke on condition of anonymity to discuss nonpublic information and a sensitive process.

The Pentagon is due for a huge boost, as President Trump promised during the campaign, but many non-defense agencies and foreign aid programs are facing cuts. The specific numbers aren’t final and agencies will have a chance to argue against the cuts as part of a longstanding tradition at the budget office.

Trump’s budget is expected in mid-March.

In an interview with Fox News Channel’s “Sunday Morning Futures,” Treasury Secretary Steven Mnuchin said cuts to Social Security and Medicare would not be part of the administration’s first budget. Trump’s priority is passing legislation to reduce middle-class and corporate taxes, he said.

The White House budget office issued a statement confirming that an interim budget submission will be released in mid-March but declining to comment on an “internal discussion.”

“The president and his Cabinet are working collaboratively to create a budget that keeps the president’s promises to secure the country and restore fiscal sanity to how we spend American taxpayers’ money,” said Office of Management and Budget spokesman John Czwartacki.

Czwartacki said the March submission would only address agency operating budgets funded by Congress, and that proposals on tax reform and so-called mandatory programs – they include food stamps, student loans, health programs and farm subsidies – will be released later.

The March release is also expected to include an immediate infusion of cash for the Pentagon that’s expected to register about $20 billion or so and contain the first wave of funding for Trump’s promised border wall and other initiatives like hiring immigration agents.

By increasing defense and leaving Medicare and Social Security untouched, the Trump final budget plan is sure to project sizable deficits. In the campaign, Trump promised huge tax cuts but top Republican leaders like House Speaker Paul Ryan of Wisconsin don’t want this year’s tax reform drive to add to the budget deficit.