Kevin Hassett, the chairman of the White House Council of Economic Advisers, said on Sunday that administration economists expected continued boosts to growth this year from the $1.5 trillion in tax cuts that Mr. Trump signed in 2017, including further increases in labor force participation by older workers.

Other economists have criticized the sustained forecast of 3 percent growth over a decade as overly optimistic. Mr. Hassett defended it by pointing to the administration’s forecast for last year, which was only slightly above the actual growth rate. “We have the same forecast we had last year,” Mr. Hassett said, “because we got last year precisely correct.”

The budget is the first of Mr. Trump’s tenure to theoretically adhere to spending caps that Congress adopted under President Barack Obama, only to bust in the years since. But Mr. Trump accomplishes this only through budgetary legerdemain by pushing much of his 4.7 percent military spending increase out of the regular budget and into an account called Overseas Contingency Operations that has been used mainly to finance wars in Iraq, Afghanistan and Syria and has therefore been exempt from congressional caps.

At the same time, domestic discretionary programs would be cut 5 percent, an idea certain to go nowhere with Democrats. Mr. Trump is hoping to avoid a repeat of last year’s budget deal, in which he was forced to agree to major domestic spending increases to secure his military boost. But he has even less sway now than he did last year, when Republicans controlled both houses of Congress.

The overseas operations fund would receive $165 billion, compared with $69 billion this year, even as Mr. Trump is scaling back military operations in Afghanistan and Syria. The last time the fund had so much money was in the 2010 fiscal year, when the United States had nearly seven times as many troops in Afghanistan and Iraq.

Among those who have criticized the overseas operations budget category as a “slush fund” is Mick Mulvaney, a Republican former congressman who served as Mr. Trump’s first budget director and is now the acting White House chief of staff.

On the wall, the president seems more intent on proving to conservatives his commitment to building it than to finding a compromise with Democrats. Administration officials said the new $8.6 billion Mr. Trump is seeking would enable him to complete the project, with a total of 700 miles of barriers, most of it new, though with some sections refurbished.