The outlines of plans to determine the fate of Lehman Brothers Holdings Inc. emerged today even as it became increasingly clear that a clean sale of the entire firm to a big bank would be too difficult to execute.

A sense of optimism that a rescue could be arranged today dimmed as a growing sense of gloom descended on Wall Street. Executives from top banks in the U.S. and Europe huddled with federal regulators in an attempt to come up with plans to either buy pieces of Lehman or prepare for an orderly winding down of the firm...