Lawrence Summers, a former Treasury secretary and senior White House economic adviser, has withdrawn as a candidate for Federal Reserve chairman in a startling development that raises urgent questions about who will lead the central bank when Chairman Ben Bernanke steps down in four months.

Summers withdrew after an intense uproar among liberal Democrats, women's groups and other advocacy organizations against his potential nomination — a highly unusual assault on the candidate whom President Barack Obama appeared to favor for the job.

Obama has said he is considering two other candidates for the post: Fed Vice Chairman Janet Yellen and former Fed Vice Chairman Don Kohn. But he was leaning toward picking Summers, people close to the White House say, and the economist's decision to take his name out of the ring might lead Obama to pursue a wider range of candidates.