WASHINGTON — [Read more on the Supreme Court’s decision on President Trump and DACA.]

Justice Department lawyers told the Supreme Court on Monday that President Trump acted lawfully in September 2017 when he decided to end an Obama-era program that protects young undocumented immigrants from deportation.

In a legal brief submitted to the court, the lawyers asserted that the president was fully within his rights to eliminate the program, known as Deferred Action for Childhood Arrivals, or DACA, and said the lower courts were mistaken when they said Mr. Trump’s action almost two years ago was arbitrary.

The Department of Homeland Security “correctly, and at a minimum reasonably, concluded that DACA is unlawful,” the lawyers argued, disputing the conclusions by the lower court judges about the three reasons the administration gave for ending the program. “None of those three grounds is remotely arbitrary or capricious, let alone all three.”

The Supreme Court is scheduled to hear arguments about the fate of the program in November. The justices could decide the case next spring or summer, just as the presidential election campaign is in full swing.