Stephen Lukasik, a physicist who sought to apply advanced technology to national security, overseeing Defense Department research on computer networking, artificial intelligence and the detection of nuclear explosions before becoming a prescient expert on cybersecurity, died Oct. 3 at his home in Falls Church, Va. He was 88.

The cause was respiratory failure, said his wife, Virginia Dogan Lukasik.

Dr. Lukasik (pronounced loo-KAY-sik) was 14 when he decided to become a physicist, haunted by newspaper accounts of the atomic bombings of Japanese cities Hiroshima and Nagasaki that ended World War II. If science had enabled humans to harness the power of nuclear fission and fusion, he decided, it could also help forestall future destruction.

Working with many others in his field, he helped develop methods to detect — and hopefully deter — nuclear explosions around the world, resulting in verification systems that proved crucial to agreements such as the Threshold Test Ban Treaty, signed by the United States and the Soviet Union in 1974.

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Through his work in the 1970s and ’80s at the Defense Department and the Federal Communications Commission, Dr. Lukasik also became a Zeligesque figure in the development of digital technologies. As the director of the Advanced Research Projects Agency, now known as DARPA, he backed the growth of ARPANET, an influential precursor to the Internet. And as chief scientist at the FCC, he helped commercialize spread-spectrum techniques, which were used for intelligence communications before becoming a cornerstone of WiFi and Bluetooth technologies.

A man of wide-ranging interests, Dr. Lukasik amassed a collection of about 15,000 books on subjects including national security, shipwrecks, archaeology and geology, and participated in a 1988 effort to date the Shroud of Turin, venerated by millions of Christians as the burial cloth of Jesus. (Radiocarbon tests indicated the frayed length of linen was created in the Middle Ages, although Dr. Lukasik cast doubts on those findings.)

His focus later shifted from nuclear weapons to cybersecurity, a field that existed in part because of the support he secured for ARPANET. The network spawned a communications revolution that played out at first in DARPA’s offices, where Dr. Lukasik encouraged the use of a system now known as email, checking messages about once an hour, often from a 30-pound “portable” computer terminal that he lugged on his travels.

In that primitive age of digital messaging, emails were generally read only through a teletype machine, which printed long ribbons of text. Dr. Lukasik, who later donated 50 boxes full of paper to the Charles Babbage Institute, was not one to throw things away. He recalled complaining to Lawrence Roberts, who ran DARPA’s Information Processing Techniques Office: “Larry, this email is great, but it’s a mess!”

“In typical Larry fashion, he came in the next day, and said, ‘Steve, I wrote some code for you that may help.’ And he showed me how to get a menu of messages, or file them, or delete them,” Mr. Lukasik said in an interview for “Where Wizards Stay Up Late,” a history of the Internet by Katie Hafner and Matthew Lyon.

“Roberts,” the authors noted, “had just written the first mail manager software.”

Long after he left DARPA, Dr. Lukasik developed a reputation as a master of “red teaming,” an apocalyptic role-playing exercise in which he imagined potential national security threats from the perspective of U.S. adversaries. Friends said he anticipated the 9/11 terrorist attacks as well as Russia’s interference in the 2016 presidential election.

“Steve would sometimes refer to his efforts as atoning for his sins, for having authorized and funded the development of an infrastructure that became a kind of threat to the country,” said Dr. Lukasik’s longtime colleague Anthony Rutkowski, referring to the conceptual model at the heart of ARPANET and the Internet.

In a phone interview, Rutkowski recalled flying home from Frankfurt to the United States on Sept. 11, 2001, while reading a report by Dr. Lukasik on the potential use of airplanes, explosives and other weapons by terrorist groups that might destroy urban infrastructure and coordinate their attacks over the Internet. “It was the most surreal thing in my life,” he said.

According to Rutkowski, Dr. Lukasik later completed a report for the Defense Threat Reduction Agency on the potential for a state actor to “marshal resources surreptitiously using social networks,” then disrupt elections and other sociopolitical institutions.

Rutkowski was unfamiliar with the report when the two friends met last year and discussed Russia’s 2016 election interference. “Bet you never envisioned that happening,” Rutkowski recalled telling Dr. Lukasik. “He said, ‘Just give me a couple of moments.’ And he went to his office, came back with this report and said, ‘Here it is, in considerable detail.’ ”

Stephen Joseph Lukasik was born on Staten Island on March 19, 1931. His father was an accountant, his mother a bank employee turned homemaker.

A collection of old scientific books at his grandparents’ home, along with stacks of science-fiction magazines, helped spark a childhood interest in the fundamental workings of the world. Steve set up a chemistry lab in his basement and entered Rensselaer Polytechnic Institute in Troy, N.Y., at 16.

Dr. Lukasik received a bachelor’s degree in physics from the school in 1951 and a doctorate from the Massachusetts Institute of Technology in 1956. He taught at the Stevens Institute of Technology in Hoboken, N.J., where he led the fluid physics division and drew the attention of DARPA, partly through a research project he managed for the Department of the Army.

DARPA hired him in 1966 to oversee research on the detection of nuclear explosions, and in 1971 he was named the agency’s director. Dr. Lukasik was credited with broadening its scope, backing research on artificial intelligence, unmanned aerial vehicles, the use of computers to hear and understand speech, and the potential for humans to influence the Earth’s climate.

Most anything was up for study, he said, with one caveat: If “you’re going to do something that looks like it’s 40,000 miles away from defense, please leave our name off of it.”

By 1975 he had left the agency, serving as chief scientist at Rand before holding the same title at the FCC from 1979 to 1982. He also worked at companies including Xerox, Northrop, TRW and SAIC.

His marriage to Marilyn Trappiel ended in divorce, and in 1983 he married Virginia Dogan Armstrong, an FCC policy analyst. In addition to his wife, of Falls Church, survivors include four children from his first marriage, Carol Ward of Boonsboro, Md., Elizabeth O’Masta of New Market, Md., Gregory Lukasik of Hagerstown, Md., and Jeffrey Lukasik of Manassas, Va.; two stepchildren, Elizabeth Armstrong Parker of Falls Church and Alan Armstrong of Atlanta; 11 grandchildren; and three great-grandchildren.

Dr. Lukasik was still called upon to consult on national security issues in recent years. And while much of his work entailed red-teaming, he never abandoned science: At 81, he was awarded a patent for an invention involving a chemical warfare sensor made with carbon nanotubes.