Rather than retire, Stone will return to Caltech, which manages the lab on NASAs behalf, university president David Baltimore said Thursday. Stone already serves as Caltechs vice president and is David Morrisroe Professor of Physics at the Pasadena, California school.

"He is going to be 65 next year and it is pretty much a rule people dont stay beyond 65 as director of JPL, so this is all very much expected," Baltimore said.

A search committee, led by Caltech trustee Adm. Bobby Inman, has already been formed to seek a replacement for Stone, who told Baltimore he would stay on as JPL director as long as necessary. Baltimore said the search could take until early 2001.

JPL has long led NASAs interplanetary exploration efforts, but has been bruised recently by the failure last year of two high-profile Mars missions, the Climate Orbiter and the Polar Lander. Baltimore said Stone began discussing stepping down last fall, but chose to delay announcing his decision.

"Because he didnt want anyone to think this was linked to the Mars failures, he waited until now," Baltimore said.

Since his first cosmic-ray experiments on the Discoverer satellites in 1961, Stone has been a principal investigator on a total of nine NASA missions and a co-investigator on five others, according to his JPL biography.

Since 1972, he has been project scientist on NASAs Voyager mission, overseeing the efforts of 11 teams of scientists in their studies of Jupiter, Saturn, Uranus and Neptune.

Stone earned his Associate of Arts degree in 1956 from Burlington Junior College before continuing his studies at the University of Chicago. After receiving his M.S. (1959) and Ph.D. (1964) degrees in physics, he joined the Caltech faculty as a research fellow in physics.

Stones tenure as director coincided with a time of large cuts to NASAs budget and employment ranks, as well as NASA Administrator Daniel Goldins push to embrace a "faster, better, cheaper" way of doing business.