Federal Reserve Vice Chairwoman Janet Yellen emerged as the front-runner to become the White House's nominee to lead the central bank, a day after Lawrence Summers pulled out of the contest amid congressional resistance, according to people familiar with the matter.

President Barack Obama hasn't made a final decision, a senior administration official said. The process for selecting a nominee isn't starting over, senior administration officials said Monday, and no new candidates have been added to the mix.

An announcement won't happen this week, officials said. White House press secretary Jay Carney said Monday that Mr. Obama is still on track to name his Fed nominee this fall, which he noted technically begins next week.

The search for a successor to Fed Chairman Ben Bernanke has become a messy public contest over the past few months after some lawmakers challenged Mr. Summers and spoke out in favor of Ms. Yellen. Mr. Obama had mentioned them both in July as candidates, along with former Fed Vice Chairman Donald Kohn.

Ms. Yellen has wide support among Senate Democrats and many fellow economists, though her support inside the White House has been shallow compared to Mr. Summers. She declined to comment Monday.