WASHINGTON — President Trump has a rocky history with the Internal Revenue Service, which he has complained audits him with unfair ferocity. Now he wants to significantly cut the tax agency’s funding at a time when it has already been bleeding staff and struggling to keep up with a flood of returns ahead of Tax Day.

The plans, revealed this week in documents associated with the White House budget outline, put Mr. Trump at odds with his Treasury secretary, Steven Mnuchin, who has argued that the I.R.S. needs more money and a larger staff.

Another round of cuts, tax experts say, could put one of the few federal departments that pay for themselves on life support.

“This is an agency that has had every last drop squeezed out of it,” said Dennis J. Ventry Jr., a member of the I.R.S. advisory council and a law professor at the University of California, Davis. “I don’t know how it’s going to sustain itself.”