O'Keefe sent a letter of resignation which was accepted by President George W. Bush, according to agency spokesman Glenn Mahone.

He was expected to leave the agency about February 1 after a successor is named, the official added.

O'Keefe is a candidate to become the chancellor of Louisiana State University.

He became administrator of the National Aeronautics and Space Administration (NASA) in 2001 with the mission of cutting costs and increasing profitability. Before NASA, O'Keefe had been the deputy head of the White House budget office.

But the Columbia disaster -- the shuttle disintegrated as it re-entered the Earth's atmosphere in February 2003 killing all seven crew -- forced a complete rethink of many NASA policies and the US space programme.

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