TOKYO — An American nuclear-powered submarine leaked radiation for more than two years, releasing the bulk of the material in its home port of Guam and at Pearl Harbor, Japanese and U.S. officials said today.

The U.S. Navy released a detailed chronology of the leaks over the past two years by the USS Houston, showing that the cumulative radioactivity released was less than 9.3 micro curies — with 8 micro curies released in Guam alone.

By comparison, according to the U.S. Environmental Protection Agency, the average amount of radioactivity in a smoke detector is about one micro curie, or 1 millionth of a curie.

The Houston, a Los Angeles-class attack submarine commissioned in 1982, is based at Apra Harbor in the U.S territory of Guam, 3,700 miles southwest of Hawai'i.

Navy Commander Jeff Davis said the Houston is still in Hawai'i being repaired and the reactor is turned off. Once the leak was discovered, the Navy provided detailed data to the Knolls Atomic Power Laboratory — a government facility — to determine exactly how much radiation had leaked over the two-year time period, Davis said.

The amount is so small, he said, that the Navy terms it a "weepage" rather than a leak. The Navy discovered the leak July 17 when a gallon of water spilled on a crew member's leg from a valve while the submarine was in dry dock for maintenance at Pearl Harbor. The water had previously come in contact with the reactor, but no radioactivity was detected on the sailor.

According to the Navy's chronology, the Houston released 8 micro curies in its home port of Guam and .4 micro curies in Pearl Harbor. In addition to the leaks in Japan — a total of .605 micro curies at the three ports — the ship also released small amounts of radiation during port visits in Singapore; Port Kelang, Malaysia; and Saipan.

The radiation leak has caused a stir in Japan where the continued presence of the U.S. military and its nuclear vessels draw complaints from residents about crime, noise and pollution linked to some 50,000 American servicemen based in the country. The presence of nuclear submarines is particularly sensitive, given that Japan is the only country the U.S. ever used atomic bombs against in the closing days of World War II.

On Aug. 1, the U.S. Navy notified Japan that the Houston had leaked the radiation during three calls to the southern Japanese ports of Sasebo and Okinawa in March and April this year but caused no threat to people or the environment.

"If we add all radiation leaked at every Japanese port, it would be still smaller than the amount of naturally occurring radioactivity found inside home smoke detectors," the Japanese foreign ministry said in a statement accompanying its release of the U.S. report. "Japan also has found no abnormality in its monitoring results during Houston's port calls since June 2006."

News of the incident also comes just weeks ahead of the arrival of the nuclear-powered aircraft carrier USS George Washington to be based in Yokosuka, just south of Tokyo.

Davis said the problem would not affect the USS George Washington's move.

"This goes to show the people of Japan and the government of Japan that they can be reassured that the United States Navy will be forthright in disclosing details about any inadvertent release of radioactivity, even when it is extremely small."

The George Washington's arrival, originally set for August under a Japan-U.S. security alliance, was delayed until late September because of a fire aboard the vessel in May, another incident that has caused safety concerns in Japan.