The US Navy said in a statement that one of its nine Nimitz-class aircraft carriers would replace the conventionally powered USS Kitty Hawk when it returns to the United States to be decommissioned.

"We believe that, through the replacement, the strong presence of the US Navy in our country will contribute to maintaining the security of Japan and maintaining the international peace and security of the Far East," Japan's Chief Cabinet Secretary Hiroyuki Hosoda told reporters.

He said it was "inevitable" that the United States' conventionally-powered aircraft carriers would eventually all be replaced by nuclear-powered ones.

The Kitty Hawk, the navy's oldest active ship, has been stationed since 1998 at the port of Yokosuka 50 kilometers (30 miles) south of Tokyo where the nuclear-powered warship will also be based.

Opposition by local residents could prove a headache for Prime Minister Junichiro Koizumi, whose hometown and constituency is Yokosuka.

Yokosuka Mayor Ryoichi Kabaya deplored that the Japanese government had made the agreement with Washington in the face of his city's opposition.

"Sudden notice was given without any consultations before and this makes us doubt how much of the city's intention had been taken into consideration and feel very regrettable," he said.

The navy said it opted for a nuclear-powered carrier because the unpredictable security environment in the western Pacific required that its most capable ships be forward deployed.

Japan's history as the only country to have been attacked with a nuclear weapon -- it was bombed by US forces in World War II at Hiroshima and Nagasaki -- has made the basing of nuclear powered warships here controversial.

The Navy said the US forces, "along with their counterparts in the Japan Self-Defense Forces, make up the core capabilities needed by the alliance to meet our common strategic objectives."

Nihon Hidankyo, a group of survivors of the atomic bombings, said that if the warship was attacked, radiation damage would be devastating.

It is "an outrageous act that offends the Japanese people who pray for peace," it said in a statement, demanding the agreement be repealed.

Officials said there had been 1,200 port visits over the years by nuclear powered warships.

But in the past, the navy has based only conventionally powered carriers in Japan because of Japanese sensitivities.

The only other conventionally-powered aircraft carrier in the US fleet, the USS John F. Kennedy, was slated for elimination in the Pentagon's proposed 2006 budget but received a temporary reprieve from Congress.

The agreement comes ahead of a set of defense consultations on Saturday that will bring top US and Japanese defense and foreign affairs officials together in Washington.

Japan and the United States reached an agreement here on Wednesday on the relocation of a controversial US air base on Okinawa island, where Tokyo said it aims to reduce the number of US troops by several thousand.

Japan's Chief Cabinet Secretary Hosoda said the planned deployment of the nuclear-powered aircraft carrier here was "nothing to do" with the relocation of Futenma air base.

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