Bruce C. Murray, a planetary geologist who won his spurs interpreting findings of early missions to Mars and who led NASA’s Jet Propulsion Laboratory through a time of flagging support for new flights in the late 1970s, died Thursday at his home in Oceanside, Calif. He was 81.

The cause was Alzheimer’s disease, said the Jet Propulsion Laboratory, which is operated for NASA by the California Institute of Technology in Pasadena. Dr. Murray was a professor emeritus at Caltech.

As director of the laboratory from 1976 to 1982, Dr. Murray faced shrinking budgets as the space agency shifted most of its resources to the emerging shuttle program. There were two Viking landings on Mars in his first year, and two Voyagers were launched to the outer planets. But prospects for any future missions were bleak.

On the brink of despair in 1981, Dr. Murray struck a defiant note in an interview with Discover magazine.