The White House had previously said that Mr. Trump would donate his salary to charity at the end of the year and suggested he would even allow reporters to decide the beneficiary. “He kindly asked that you all help determine where that goes,” Mr. Spicer said last month. “The way that we can avoid scrutiny is let the press corps determine where it should go.”

Mr. Spicer did not explain on Monday why the plan had changed, but said the White House Counsel’s Office presented a series of alternatives to the president and he chose the National Park Service.

“The park service has cared for our parks since 1916, and the president is personally proud to contribute the first quarter of his salary to the important mission of the park service, which is preserving our country’s national security,” Mr. Spicer said.

But in picking a government agency, Mr. Trump chose one with a large backlog of deferred maintenance that could be deferred even longer under his budget. Mr. Trump proposed a cut of $1.5 billion, or 12 percent, from the Interior Department, which oversees the park service and other agencies. The proposal did not specify how much of that would come out of the park service budget.

He also chose an agency with which he has had a fraught relationship. Mr. Trump was angry when a park service employee using an agency Twitter account reposted information comparing the size of his Inauguration Day crowd unfavorably with that of former President Barack Obama in 2009. Mr. Trump was livid and called the acting director of the park service the day after his inauguration to complain about the post and to ask for further photographic evidence about the size of his crowd.