WASHINGTON — President Obama nominated Judge Merrick B. Garland to the Supreme Court to help enhance the reputation of an institution whose public approval has dropped substantially in this era of heightened political polarization, he said in an interview with National Public Radio.

Judge Garland “would help to burnish the sense that the Supreme Court is above politics and not just an extension of politics, and would set a good tone for restoring — or at least increasing — the American people’s confidence in our justice system,” Mr. Obama said in an interview with NPR’s Nina Totenberg.

The interview signaled the start of what is expected to be an aggressive campaign by the White House and outside groups to promote Judge Garland as a peerless jurist who deserves a hearing and a vote on his nomination by the Senate.