William J. Thaler, 79, a Georgetown University physicist who was a hero of the period when Americans were gravely worried about the threat of Soviet missiles and nuclear attacks, died of a stroke June 5 in his Centreville home.

Dr. Thaler burst onto the public scene like a supernova in 1959 when the Defense Department announced that the 33-year-old Navy physicist had discovered a way for radar to "see" over the horizon to detect enemy missiles up to 5,000 miles away.

The electronic system detected the ionized gases of a missile launch or an atomic explosion by bouncing radar waves off the ionosphere, the thick layer of charged particles around the Earth. The work was dubbed "Project Teepee" for "Thaler's project."

He previously had directed the Office of Naval Research portion of the secret Argus Project, in which atomic bombs were exploded 300 miles above the South Atlantic to study the impact of high-altitude nuclear explosions on radio transmissions and radar operations, and to increase the understanding of the geomagnetic field and the behavior of the charged particles in it. At the time, the military called it "the biggest scientific experiment ever undertaken."

The subject of adoring articles in the news media, the Baltimore native was described as a handsome six-footer who drove a quirky, bright-red BMW Isetta, loved beer, pretzels and television Westerns, read science fiction and "laughs at the comics every morning."

"My branch is a kind of hush-hush, free-wheeling, idea group specializing to some extent in the bizarre," he told the New York Times in 1959. "I can walk down the halls and get reports on basic research in chemistry or electronics or what have you, all of which can stimulate your thinking along oddball lines. I can do anything my little heart desires. I can dream big and plan big, and if the dream and the plan are reasonable enough and show enough promise, I can get the money to go ahead."

Dr. Thaler did not try to cash in on his fame. He turned down a $40,000 job offer from private industry in 1960 because he thought a $12,000 teaching and research post at Georgetown would let him be more creative. But he became a scientist almost by accident.

After graduating in 1943 from Loyola High School in Towson, Md., where he and his four brothers were known as tennis champions, Dr. Thaler had to wait a year before he could take flight training with the U.S. Army Air Forces. He enrolled in Loyola College in Baltimore to get some science background to supplement his interest in Latin and Greek languages. By the time he finished his training, World War II had ended. He never went back to language study.

After graduating from Loyola, he received a master's degree in physics in 1949 and a doctorate in physics in 1951 from Catholic University. He went to work for the Office of Naval Research, where his primary work was in nuclear weapons effects test planning and execution. Dr. Thaler participated in every nuclear weapons test at Eniwetok Atoll and in Nevada from 1952 to 1960.

After he achieved a measure of fame, Dr. Thaler urged high school students to consider physics as a career, adding that "you don't have to be a genius or a near-genius" to be good at the work. "Everyone thinks that a physicist has to be sort of super-duper, and that's not so at all," he told The Washington Post in 1964. He suggested that the 12 elementary and secondary school grades be compressed into nine because he was convinced that "the average student" could cover the material that quickly and "maybe 15 percent" of them could then go straight to college.

At a time when Americans seemed to ricochet between fear of a nuclear Armageddon and anticipation of intergalactic travel, Dr. Thaler tried to reassure the public.

The conquest of space, he said in a 1961 speech to the Georgetown University Club, is a "logical substitute for war."

"Man has always looked enviously at the stars, and here certainly is an adversary worthy of his energies, imagination and aggressiveness," he said. "Indeed, if we ever do succeed at the conference table in a controlled, foolproof disarmament, simple economic considerations will demand a substitute for all the vast industrial efforts presently devoted to national defense."

After taking the job as chairman of Georgetown's physics department, Dr. Thaler taught and did research for 15 years. In 1967, he sought a patent for a device used to communicate sound over a laser beam. He ran unsuccessfully as a Republican for the Centreville seat on the Fairfax County Board of Supervisors in 1967 and 1971.

In 1975, he took the chief scientist's job at the White House Office of Telecommunications Policy. He returned to Georgetown in 1978 after President Jimmy Carter abolished the telecommunications office. He retired in 1996.

Dr. Thaler was awarded the Villanova University Mendel Medal in 1960. He was a member of the Cosmos Club. At age 13, he won the Middle-Atlantic boys tennis championship, and as an adult, he won the Maryland doubles tennis tournament five times.

A son, Geoffrey Andrew Thaler, died in 2003.

Survivors include his wife of 54 years, Barbara Thaler of Centreville; four children, Paul Thaler of Rixeyville, Va., Gregory Thaler of Herndon, Peter Thaler of Gainesville and Alice Thaler of Thurmont; and nine grandchildren.

William J. Thaler, former chairman of Georgetown's physics department, discovered a way for radar to detect missiles 5,000 miles away.