CHICAGO  President-elect Barack Obama said Thursday afternoon that he selected Representative Rahm Emanuel, a fierce and consummate navigator of the capital’s political terrain, as his chief of staff because he has “deep insights into the challenging economic issues that will be front and center for our administration.”

“I announce this appointment first because the chief of staff is central to the ability of a president and administration to accomplish an agenda,” Mr. Obama said in a statement. “And no one I know is better at getting things done than Rahm Emanuel.”

A veteran of the Clinton administration and a fellow member of Congress from Illinois, Mr. Emanuel has been a close adviser to Mr. Obama. He informed Mr. Obama of his decision on Thursday morning, saying he would step down as the fourth-ranking Democrat in the House of Representatives to help guide the Obama administration.

“Now is a time for unity,” Mr. Emanuel said. “I will do everything in my power to help you stitch together the frayed fabric of our politics, and help summon Americans of both parties to unite in common purpose.”