Richard Feynman, 69, a professor of theoretical physics at the California Institute of Technology and a winner of the 1965 Nobel Prize for physics, died of cancer Feb. 15 at the UCLA Medical Center in Los Angeles.

In 1986, Dr. Feynman served on the 13-member presidential panel that investigated the Challenger space shuttle disaster. In that role, he exhibited the same independence, bumptious brilliance and seemingly unquenchable thirst for answers to puzzles that had characterized his life in science and teaching.

His 1985 autobiography, "Surely You're Joking, Mr. Feynman," was on the New York Times best-seller list for 14 weeks. The book described his work on the atomic bomb at Los Alamos in World War II. He amused himself there in the desert by "cracking" office safes and leaving them open to be found by irate security personnel.

The book also covered such events as Dr. Feynman's periodic visits to the gambling emporiums of Las Vegas and it gave his detailed advice on the best way to pick up girls. It also told of visits to Brazil, where he devoted nearly equal attention to physics and bongo playing.

Dr. Feynman shared the 1965 Nobel Prize for physics with Julian S. Schwinger of Harvard University and Japan's Shinichiro Tomonaga for their work in developing an improved theory of quantum electrodynamics. During the 1940s, the three worked independently on problems in the field, which describes the standard processes of radiation occurring in atomic physics.

Their contributions allowed scientists to predict the effects of electrically charged particles on each other in a radiation field.

A statement issued by Caltech said that as a result of Dr. Feynman's work, "by 1965, modern quantum electrodynamics had brought order to that vast part of physics lying between gravity and nuclear forces, and his simplified rules of calculation had become standard tools of theoretical analysis in both quantum electrodynamics and high-energy physics."

He helped quantum electrodynamics become one of the most highly developed areas of physics. The Feynman diagrams, used in measuring changes in subatomic particles, were not only accurate but elegant. His work held deep consequences for elementary particle physics and affected advances in computer science.

In recent years, Dr. Feynman had been a leader in research into subatomic particles, the study of the building blocks of protons and neutrons. Probably more than any other scientist, he shaped the mathematics used in discussing particle physics.

On Jan. 28, 1986, the space shuttle Challenger exploded shortly after its launch, killing all seven astronauts, including New Hampshire schoolteacher Christa McAuliffe. Dr. Feynman was named to the commission to examine the disaster and report on its cause and the ways safety could be improved.

He became a caustic critic of NASA, citing its erratic attention to safety matters. Rather than take part in committee hearings, he conducted his own one-man investigation. At one point it was said that the explosion was triggered by failure of chilled "O rings" to effectively seal the booster.

When a NASA official said this would be impossible to test, Dr. Feynman got a glass of ice water, fastened O ring material to the glass under the water's surface, and proceeded to demonstrate that the material deteriorated. His "Personal Observations on the Reliability of the Shuttle" was published as an appendix to the presidential report.

His other works included "The Feynman Lectures on Physics," a three-volume classic that appeared in 1963, "The Character of Physical Law" and the "QED: The Strange Theory of Light and Matter," both written for a broader audience.

Richard Phillips Feynman was born in New York City. His father began teaching mathematics to him when he was a toddler. Dr. Feynman, as a boy, taught himself calculus. He was a 1939 honors graduate of the Massachusetts Institute of Technology and received his doctorate in theoretical physics from Princeton University in 1942.

He worked at the Frankfort Arsenal in Philadelphia before going to Los Alamos to work on the first atomic bomb. He became a group leader under Hans Bethe and worked with such other giants as Enrico Fermi and Niels Bohr. He was a witness to the first detonation of the bomb in July 1945.

After the war, he taught at Cornell University before becoming a full professor at Caltech in 1951. A provocative, demanding and much-admired teacher who always taught freshmen as well as the most advanced classes, he once said, "Hell, if I could explain my work to the average person it wouldn't be worth the Nobel Prize."

He also appeared in school plays, once taking the role of a bongo player in the musical "Guys and Dolls."

In addition to the Nobel Prize, his honors included the Institute for Advanced Study's Albert Einstein Award, the Atomic Energy Commission's E.O. Lawrence Award, the Niels Bohr International Gold Medal and the Albert Einstein College of Medicine's Einstein Award. In 1982, the students of Caltech gave him a teaching award,

His first wife, the former Arline H. Greenbaum, died in 1945. His second marriage, to the former Mary Lou Bell, ended in divorce.

Survivors include his wife, Gweneth, whom he married in 1960, their two children, and one sister.