BERLIN – Nazi scientists trying to build an atomic bomb set off a test explosion two months before the end of World War II, killing hundreds of people in eastern Germany, a German researcher claims in a book published yesterday.

“Hitler’s Bomb” theorizes that the March 1945 device didn’t achieve fission, but did scatter telltale radioactive particles at the Ohrdruf test site. It also claims that Nazi Germany briefly had a working nuclear reactor, something historians generally dispute.

Author Rainer Karlsch, an economic historian, offers no firsthand proof, saying his account is an interpretation of available evidence and he hopes it will spur more research.

He said soil samples from the Ohrdruf site he had analyzed for his book turned up above-average levels of radioactive isotopes such as cesium 137 and cobalt 60, though he quotes the testers as saying the site poses no radiation hazard.

However, access to what he believes was ground zero was barred because of old munitions at the site, which served as a Soviet military training area in East Germany after the war. An American mission that arrived in Germany with American troops in 1945 to investigate the German atomic bomb program concluded that the Germans were nowhere near making a nuclear weapon.

Mr. Karlsch doesn’t claim they were near. But based on witness accounts recorded after the war, postwar Allied aerial photos, and Soviet military intelligence reports, he argues that a test blast happened March 3, 1945, at Ohrdruf – then being run as a Nazi concentration camp. He says there probably were several previous tests.

“Hitler’s bomb – a tactical nuclear weapon with a potential for destruction far below that of the two American atomic bombs – was tested successfully several times shortly before the end of the war,” the book says.

A professor of physics and the history of science at Harvard University, Gerald Holton, said the main scientists in the Nazi atomic bomb program never mentioned a test blast or having built a working nuclear reactor.

British intelligence bugged the scientists – including a key planner, Walther Gerlach – while they were interned at Farm Hall manor in England after the war.

Any claims of a Nazi test blast “would have to have a lot of documentary evidence behind it,” Mr. Holton said.

“It also would have to be checked against the remarks that Gerlach made during his period at Farm Hall … where none of that sort of planning was discussed by him or anyone else.”

Mr. Karlsch says scientists around Gerlach had “a certain amount” of enriched uranium from an as yet unknown source. The German device probably was a 2-ton cylinder containing enriched uranium, he writes. The amount of uranium was small, meaning the conventional explosives used to trigger the device did not set off a vastly more destructive nuclear chain reaction, Mr. Karlsch said.

That would mesh with an account Mr. Karlsch said he found in Soviet military archives, apparently based on information from a German informant, that said the blast felled trees within a radius of about 500 to 600 yards.

Witnesses reported a bright flash of light and a column of smoke over the area that day, and residents said they had nausea and nosebleeds for days afterward, Mr. Karlsch says.