By Kristina Peterson and Nick Timiraos

WASHINGTON -- President Donald Trump's first budget will seek a large increase in military funding but won't make changes to the largest future drivers of government spending: Social Security and Medicare.

Work to prepare the president's first budget proposal, expected to be released in mid-March, ramped up last week following the Feb. 16 confirmation of Mick Mulvaney as director of the Office of Management and Budget.

The White House plans to send federal agencies their proposed budget allocations on Monday, a person familiar with the matter said. Mr. Trump will preview some of the budget priorities in his speech to Congress on Tuesday and release a budget outline in mid-March after gathering information from federal agencies.

The president's budget proposal marks the opening of the monthslong process to set funding levels for the following year. Spending bills originate with Congress and need 60 votes to clear procedural hurdles in the Senate.

In his address to Congress, Mr. Trump also is expected to emphasize two of his top legislative priorities: simplifying the tax code and dismantling the Affordable Care Act and replacing it with something else, White House officials said Sunday.

Speaking Sunday on Fox News, Treasury Secretary Steven Mnuchin said the budget outline won't include any changes to entitlement spending programs. "We are not touching those now. So don't expect to see that as part of this budget," he said.

Mr. Mnuchin, in an interview last week, said an increase in military spending "is an important priority, and I think it's likely that you'll see that reflected in the president's budget."

By pushing for more military funding and taking entitlement spending changes off the table, the Trump administration also would need to propose funding cuts for nondefense programs to avoid sending deficits much higher.

Mr. Trump, for example, is expected to seek cuts at the Environmental Protection Agency and in other areas of domestic spending.

Congressional Republicans have said they would look to Mr. Trump's speech for hints about the first budget proposal his administration will send to Capitol Hill, expected in mid-March.

Although Mr. Trump repeatedly said on the campaign trail he didn't want to reduce spending on Medicare or Social Security, Mr. Mulvaney has long advocated for sharply lowering federal spending, including on entitlement programs.

Given that Mr. Trump plans to boost military spending and cut taxes, the White House budget plan could leave conservatives in a difficult position if the GOP-led budget does little to curb spending.

"You have got to pay for those things. We've got to pay for those things, " Rep. Jim Jordan (R., Ohio), an influential conservative lawmaker, said Sunday on ABC. Conservatives generally want to cut spending on entitlements to offset more military spending.

On Tuesday night, the president is also expected to generally outline his priorities on health policy. He said earlier this year that his goal was to provide "insurance for everybody." White House deputy press secretary Sarah Huckabee Sanders declined Sunday to guarantee that no one would lose his or her current coverage under the GOP plan.

"I know that the goal is that we make sure that people don't lose their coverage and that we have to put a high priority on people that need it most," Ms. Sanders said on ABC.

Republicans are also split over how to overhaul Medicaid, the federal-state insurance program for the poor, which some states expanded under the 2010 health law.

In Tuesday's speech, Mr. Trump also will likely reiterate his desire to increase border security, his former campaign manager, Corey Lewandowski, said Sunday on Fox.

Mr. Trump campaigned for president promising a full wall along the border with Mexico and continues to talk about building it. But he is running into resistance from some Republicans in Texas.

Write to Kristina Peterson at kristina.peterson@wsj.com and Nick Timiraos at nick.timiraos@wsj.com

(END) Dow Jones Newswires

February 26, 2017 21:36 ET (02:36 GMT)

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