WASHINGTON - Ralph E. Lapp, a physicist who was involved in atomic weapons from the earliest days of the Manhattan Project, was a prominent figure in the Cold War debate about civil defense, and continued to speak out about the health effects of radiation into the 1990s, died Tuesday in Alexandria, Va. He was 87.

The cause was pneumonia after surgery, his family said.

In December, 1942, when Enrico Fermi was preparing the first demonstration of a human-made nuclear chain reaction in a squash court under the stands at Stagg Field at the University of Chicago, Mr. Lapp was studying cosmic rays with equipment housed in the stadium's press box.

He later wrote that he was lugging a Geiger counter down from the box and "soon found myself inside the stands amid other white-jacketed men," who were working with the nuclear reactor.

His son Dr. Christopher W. Lapp said his father had told the family that he sneaked into the room, introduced himself as a physicist, and was put to work.

After the war, Mr. Lapp was hired by the Manhattan Project's successor agency, the Atomic Energy Commission, and became assistant director at its Argonne National Laboratory, the nuclear research laboratory operated for the government by the University of Chicago. He left the government in 1950 and became a private consultant on nuclear issues.

In that capacity, he wrote more than 20 books and numerous magazine articles, many on the theme that while nuclear war was a profound threat, the dangers of radiation were often overstated.

Mr. Lapp spoke in Toledo and the area more than a half-dozen times, from 1956 to 1979.

During these appearances he often addressed several themes. Favorites included excess government secrecy and the risks of nuclear war.

In 1956 in Lima, Ohio, for example, he scorned what he saw as a veil of governmental secrecy thrown over scientific projects.

He also called for controls on nuclear weapons testing.

The next year in Toledo, he warned about the risk of nuclear war with the Soviet Union and called for finding a way of settling disputes peacefully.

In November of 1957, speaking at Collingwood Temple, he criticized the lack of basic science education in the United States and warned about indiscriminate use of X-rays and radioactive isotopes in medicine and dentistry as hazards to health.

In 1958, he told Toledo teachers the nation must have a cabinet-level department of science to spur research in order to compete with Russia.

At the University of Toledo in 1972, he proposed construction of offshore nuclear power plants as a long-range solution to power shortages.

Four years later, at a session on regional energy strategies, he complained that what he called reckless criticism by some scientists was confusing the public about the risks of nuclear power and hindering the development of nuclear power.

Besides his son Christopher, he is survived by his wife of 48 years, Jeannette, and another son, Nicholas.

First Published September 11, 2004, 9:41 a.m.