Paul Leventhal, 69, founder of the Nuclear Control Institute in Washington and an expert in nuclear proliferation issues, died April 10 at his home in Chevy Chase. He had melanoma, a form of skin cancer.

Mr. Leventhal, a former newspaperman and congressional aide, launched his advocacy institute with a full-page ad in the New York Times on June 21, 1981, posing the question: "Will Tomorrow's Terrorist Have an Atom Bomb?"

Since serving in the early 1970s as an aide on a Senate subcommittee chaired by Sen. Abraham Ribicoff (D-Conn.), Mr. Leventhal remained adamant about the dangers of nuclear terrorism and global commerce in plutonium -- a key element used in nuclear weapons -- and worked to prevent the spread of nuclear weapons to nations or groups.

On the subcommittee, Mr. Leventhal worked on a Nixon administration bill to reorganize the Atomic Energy Commission. He described work on the legislation as a "baptism in fire" that changed his life.

Mr. Leventhal, who worked in the Senate from 1972 to 1981, was responsible for the investigations and legislation that resulted in passage of two landmark nuclear laws -- the Energy Reorganization Act of 1974, which split the Atomic Energy Commission into separate regulatory and promotional nuclear agencies, and the Nuclear Non-Proliferation Act of 1978, which established stricter controls on U.S. nuclear trade.

The non-proliferation act's requirement that countries accept international inspections on all their nuclear activities -- "full-scope safeguards" -- as a condition for receiving U.S. nuclear assistance eventually was adopted as an international norm by the multinational Nuclear Suppliers Group.

Mr. Leventhal recognized the growth and threat of nuclear and bomb-grade materials, said lawyer Richard Wegman, who served as chief counsel for Ribicoff's committee with Mr. Leventhal and later as counsel for the Nuclear Control Institute.

"Paul was a truly remarkable individual, exceptionally dedicated to an exceptionally difficult cause," Wegman said. "He was one of the first to work for full-scope safeguards. . . . He insisted on incorporating that concept in legislation."

In 1979, Mr. Leventhal served as co-director of the bipartisan Senate investigation of the Three Mile Island nuclear accident, and he prepared the "lessons-learned" legislation enacted in 1980 to require preventive measures and emergency planning.

He said that work left him "acutely aware of that ineffable combination of human fallibility and mechanical failure that makes nuclear plants vulnerable to accidents, and also sabotage."

He lamented a few years ago that the flow of nuclear technology and materials from industrial countries to developing regions was continuing.

"As a result, there is now more plutonium in civilian hands than in all of the nuclear weapons in the world. And some of it has already been turned into bombs, as in India, Pakistan and North Korea, while others have used or are now using civilian nuclear programs as a cover for weapons programs," he said in a speech in 2001, adding that Iran and Iraq raised immediate concerns.

Mr. Leventhal, born in Manhattan, graduated magna cum laude with a degree in history from Franklin & Marshall College in Pennsylvania in 1959 and received a master's degree from the Columbia University Graduate School of Journalism in 1960. He spent 10 years as an investigative and political reporter at the Cleveland Plain Dealer, the New York Post and Newsday, until deciding that he wanted to "get inside of government and try to make it work."

In 1969, he came to Washington as a press secretary to Sen. Jacob K. Javits (R-N.Y.), served in 1970 as campaign press secretary to Sen. Charles Goodell (R-N.Y.) and two years later was a congressional correspondent for the National Journal.

From 1972 to 1976, he concentrated on nuclear weapons proliferation as a research fellow at Harvard University's Program for Science and International Affairs and as a visiting fellow at the Brookings Institution. From 1979 to 1981, he was staff director of the Senate Nuclear Regulation Subcommittee, chaired by Sen. Gary Hart (D-Colo.).

After starting the Nuclear Control Institute, Mr. Leventhal served as its president for 22 years, lectured in a number of countries, organized conferences and wrote op-ed articles and books on nuclear terrorism, averting a Latin American nuclear arms race, nuclear power and the spread of nuclear weapons.

For the past several years, he directed the institute as a Web-based program that maintains a word-searchable electronic archive at http://www.nci.org and a collection of institute and Senate papers spanning more than 30 years at the National Security Archive.

Survivors include his wife, Sharon Tanzer Leventhal of Chevy Chase; two sons, Theodore Leventhal of Washington and Joshua Leventhal of Raleigh, N.C; a brother; and two grandsons.