President Donald Trump has unveiled a $US1.15 trillion budget, a far-reaching overhaul of federal government spending that slashes many domestic programs to finance a significant increase in the military and make a down payment on a US-Mexico border wall.

Trump's proposal on Thursday seeks to upend Washington with cuts to long- promised campaign targets like foreign aid and the Environmental Protection Agency as well as strong congressional favourites such as medical research, help for homeless veterans and community development grants.

"A budget that puts America first must make the safety of our people its number one priority - because without safety, there can be no prosperity," Trump said in a message accompanying his proposed budget titled: America First: A Budget Blueprint to Make America Great Again.

The $US54 billion boost for the military is the largest since President Ronald Reagan's Pentagon buildup in the 1980s, promising immediate money for troop readiness, the fight against Islamic State militants and procurement of new ships, fighter jets and other weapons. The 10 per cent Pentagon boost is financed by $US54 billion in cuts to foreign aid and domestic agencies that had been protected by former President Barack Obama.

The budget goes after the frequent targets of the party's staunchest conservatives, eliminating the National Endowment for the Arts, legal aid for the poor, low-income heating assistance and the AmeriCorps national service program established by former President Bill Clinton.

Lawmakers will have the final say on Trump's proposal in the arduous budget process, and many of the cuts will be deemed dead on arrival.

Law enforcement agencies like the FBI would be spared, while the border wall would receive an immediate $US1.4 billion infusion in the ongoing fiscal year, with another $US2.6 billion planned for the 2018 budget year.

Trump repeatedly claimed during the campaign that Mexico would pay for the wall when, in fact, US taxpayers will foot the bill.

Trump's proposal covers only roughly one-fourth of the approximately $US4 trillion federal budget, the discretionary portion that Congress passes each year.