WASHINGTON —  An air sampling taken after North Korea's claimed nuclear test detected gaseous radioactive debris consistent with an atomic explosion, Bush administration and congressional officials said Friday night. They said no final determination had been made about the nature of last weekend's mystery-shrouded blast.

One congressional official said that radioactive material was found in an air sample collected on Wednesday. It was one of several tests to determine the validity of North Korea's claim that it had set off a nuclear test.

"The betting is that this was an attempt at a nuclear test that failed," another official said. "We don't think they were trying to fake a nuclear test, but it may have been a nuclear fizzle." The officials who described the results spoke on condition of anonymity because of the sensitive nature of the information.

The administration briefed key members of Congress about the preliminary test results. One official said the sample was collected above Qunggye, near the area of the claimed nuclear test.

CountryWatch: North Korea