In an appointment that is being read as everything from a coup for women to a sign of internecine warfare over the future of the Energy Department, Martha O. Hesse was appointed yesterday as assistant secretary of energy for management and administration.

Hesse, whose recess appointment becomes effective immediately, becomes the department's highest-ranking woman. She also shoulders aside the current assistant secretary, William S. Heffelfinger, a man with powerful friends and possibly even more powerful enemies.

Yesterday's announcement notes, without elaboration, that Heffelfinger resigned his job, but sources inside the department speculated that he might regain his old title as director of administration. There were some indications that he was forced out because of what higher-ups interpreted as his foot-dragging on the administration's reorganization plan for DOE.

Hesse, on the other hand, is a highly regarded administrator who has worked closely in two previous jobs with Joseph R. Wright, now deputy director of the Office of Management and Budget and one of the administration's most ardent advocates of dismantling DOE. Hesse worked for Wright both at OMB, as executive director of President Reagan's new task force on management reform, and earlier at the Commerce Department.