By Diane Bartz

WASHINGTON, Feb 22 (Reuters) - Federal Trade Commission Chairman Jon Leibowitz, who had been expected to step down on Feb. 15, has extended his tenure into next week, FTC spokesman Peter Kaplan said.

A replacement for Leibowitz, who has been at the agency for eight years, has yet to be named. Leibowitz became a commissioner in 2004 and chairman in March 2009.

During his term, the FTC investigated allegations that Intel Corp and Google Inc broke antitrust law. It also won multimillion-dollar settlements from Skechers USA Inc and Reebok, which is owned by Adidas AG, for advertising "toning shoes" with unfounded claims the footwear would enable users to get stronger.

Leibowitz has been energetic in fighting deals that brand-name pharmaceutical companies make with generic drugmakers to delay the manufacture of cheaper versions of best-selling drugs.

The U.S. Supreme Court is due to take up these "pay for delay" arrangements in an oral argument next month.

Candidates to succeed Leibowitz are Commissioners Julie Brill and Edith Ramirez; Howard Shelanski, director of the FTC's Bureau of Economics; and Philip Weiser, a veteran of the White House and Justice Department who now teaches law at the University of Colorado in Boulder.

Brill and Ramirez would not face confirmation by the Senate and are considered front-runners. Any new commissioner would require Senate confirmation, which could easily take several months.

Without Leibowitz, a Democrat, the agency will have two remaining commissioners from each party. This raises the possibility of a string of deadlocked 2-2 votes.

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