While the line of succession from President to Vice President to Speaker of the House, etcetera, is the long-established law of the land, there is no similar requirement applying to federal agency heads.
But that’s about to change.
President Bush has ordered all agencies to "establish, maintain, and, as necessary, revise an order of succession," or to propose that the President establish one for them.
The reason: Each agency must be able to discharge its duties no matter what has happened to its chief by dying, resigning or otherwise becoming unable to carry out his or her duties, said President Bush on the anniversary of the September 11, 2001 attacks.