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.

"We're sitting here watching the coffin being nailed shut, and what's inside is imagination and vision," he said. "I wasn't appointed director to preside over the dissolution of the U.S. space exploration program. I'm not going to be squeezed down to nothing."

Those were tough years, both for him and for the laboratory. In a New York Times Magazine article, the science writer Timothy Ferris described Dr. Murray as a "square-jawed man more comfortable giving orders than listening to advice," adding that he "brought to the lab an aggressive — some would say abrasive — style of leadership under which its fortunes have sharply improved."

John Casani, a retired project manager at the laboratory, told The Associated Press: "People at J.P.L. either loved or hated him. He was always shaking cages."

Through persistence, he kept the doors open. He managed to salvage a Jupiter orbital mission, later named Galileo, an imaging radar system for Earth mapping to be flown on space shuttles, an early Earth-observing satellite called Seasat and a joint project with Britain and the Netherlands called the Infrared Astronomy Satellite.

Out of concern for the future of planetary exploration, Dr. Murray joined with the astronomer Carl Sagan and the aerospace engineer Louis Friedman to found the Planetary Society, a public advocacy organization dedicated to exploring the solar system and searching for extraterrestrial intelligence. The society, based in Pasadena, has reported some 100,000 members. Dr. Murray was its retired chairman.

"We seem to have the idea that the space age started and ended with one generation," he said in an interview at the time. "We go to the planets and have a look and then walk away and do nothing."

Bruce Churchill Murray was born Nov. 30, 1931, in New York City. His family later moved to California, and he graduated from Santa Monica High School. He was educated at the Massachusetts Institute of Technology, where he earned a Ph.D. in geology in 1955.

After working as a geologist for Standard Oil, he spent two years in the Air Force as a geophysicist and then became a researcher at Caltech in 1960, at a time of growing excitement over space exploration.

He joined the faculty as an associate professor of planetary science in 1963, and became a member of the science team for Mariner 4, the first successful flyby of Mars, in 1965.

Those first pictures of a moonlike Mars of cratered plains were a disappointment to those who grew up imagining Martians. But further flyby exploration by Mariners 6 and 7, and especially Mariner 9's orbital survey in 1971-72 — all with Dr. Murray on the science team — began to reveal a more diverse Mars of mountains and canyons, with some evidence of water erosion in the distant past. He constructed a geologic history of Mars from these images.

From his Mars experience and as chief scientist for the Mariner 10 mission to Venus and Mercury, as well as his budget battles as the J.P.L. director, Dr. Murray wrote a popular book, "Journey Into Space: The First Thirty Years of Space Exploration," in 1989. He also collaborated with Arthur C. Clarke, Ray Bradbury and Walter Sullivan on another book, "Mars and the Mind of Man," based on a symposium conducted at the time that Mariner 9 swept into an orbit of Mars.

He published more than 130 research papers and four other books as well, and was the associate director of an award-winning educational film, "Mars Minus Myth," first released in 1973 and revised in 1977.

His survivors include three children, Christine, Stephen and Peter, from his first marriage, to the former Joan O'Brien. They were divorced in 1970. The next year he married Suzanne Moss, who survives, as well as her daughter, Allison, whom Dr. Murray adopted; their son, Jonathan; and 11 grandchildren.

In a television interview in 1989, Dr. Murray spoke of the lingering disappointment of his experience as the Jet Propulsion Laboratory's director.

"I went into J.P.L. full of hope that I could reverse the trend of backing away from space exploration — which started in '72 and by the time I got there in '76 was in full steam — and found I couldn't," he said. "I could alleviate the effects somewhat and kind of dampen it, but I couldn't change the trend. That was pretty upsetting."

Afterward, Dr. Murray said: "I had to decide what I wanted to do, and I tried some things and came to the conclusion what I enjoy more than anything else in the world is teaching and working with graduate students doing research. That is really satisfying."

So he returned to the Caltech faculty and served on the science teams for other Mars missions in the 1990s. On his retirement in 2001, he was made professor emeritus of planetary science and geology.