The easy part of newly assigning a U.S. aircraft carrier to Japan, which was to persuade the Japanese to accept a nuclear-powered vessel, has been accomplished. Now comes the hard part, deciding which one of 10 carriers should be based in the port of Yokosuka.

Deployments of the world's mightiest warships are not to be taken lightly.

They are the most visible symbols of American ability to project sea power and to maintain a presence far from U.S. shores. In a crisis, often the first question from the White House is: "Where are the carriers?"

Indeed, deciding which carrier to base in Japan is so complicated that it may go all the way to President Bush. The move must take into account Japanese attitudes, U.S. military strategy, and American politics and economics — much of which will be difficult to reconcile.

At the moment, the leading candidates would seem to be the USS Abraham Lincoln, named for the American perhaps most revered in Japan, and the USS George Washington, named for the father of his country. The Lincoln, based in Bremerton, Wash., belongs to the Pacific Fleet while the Washington is assigned to the Atlantic Fleet and is based in Norfolk, Va.

Among carriers that should not be under consideration are the USS Harry S Truman, named for the president who ordered the atomic bombings of Hiroshima and Nagasaki in 1945 to get Japan to surrender and end World War II, and the USS Nimitz, named for the U.S. naval commander, Admiral Chester Nimitz, in that war against Japan.

Posting the USS Dwight D. Eisenhower to Japan would recall the cancellation of President Eisenhower's visit to Tokyo in 1960 in the face of violent protests against the U.S.-Japan Security Treaty. The USS Enterprise, the first nuclear-powered carrier to visit Japan, stirred up similar protests in Sasebo, a port in southwestern Japan, in 1968.

The USS Theodore Roosevelt is named for the president who negotiated a treaty to end the Russo-Japanese War of 1904-1905 that many Japanese thought unfair. The USS John C. Stennis and USS Carl Vinson are named for chairmen of the Senate Armed Services Committee unknown to most Japanese.

Finally, the USS Ronald Reagan would get an indifferent reception.

Triggering this search is the need to replace the USS Kitty Hawk, the conventionally powered carrier based in Yokosuka now. It is to be retired in 2008. The USS John F. Kennedy, based in Mayport, Fla., is also conventionally powered and is to retire shortly after.

After months of quiet negotiations, U.S. diplomats recently got an agreement from Japan that the Kitty Hawk's replacement would be nuclear powered. The "nuclear allergy" of Japan that is the legacy of the atomic bombings appears to be fading. Moreover, nuclear plants generate a third of Japan's electricity today.

Secretary of Defense Donald Rumsfeld is preparing a report for Congress known as the Quadrennial Defense Review that officials say will reflect a shift in U.S. power from the Atlantic to the Pacific caused by the rise of China, the belligerence of North Korea, piracy in vital sea lanes of Southeast Asia and the threat of terror.

The report, to be delivered early next year, will call for shifting a carrier from the Atlantic to the Pacific so that six of those 90,000-ton warships, each carrying 85 fighters, bombers and other aircraft, and each operated by 5,500 sailors and aviators, will be posted in the Pacific and four in the Atlantic. The sixth Pacific carrier would most likely be based at Pearl Harbor.

Here's where politics weigh in. The five carriers based in Norfolk are under the vigilant eye of Sen. John Warner, chairman of the Armed Services Committee. He is a Republican as is Virginia's other senator, George Allen, and five of the state's eight representatives.

Rumsfeld will find it hard to persuade Republican allies to give up a ship that brings dollars and jobs into their electoral districts. Ship maintenance, supplies and spending by the crews all pump large sums into economies around naval bases. Even so, sending one of the five carriers from Norfolk to Hawai'i or Japan would seem to be on the horizon.

In contrast, the senators from California, Barbara Boxer and Dianne Feinstein, and from Washington state, Maria Cantwell and Patty Murray, are Democrats critical of the Bush administration. Their pleas to keep ships in San Diego or Bremerton are not likely to be given much weight.

Richard Halloran is a Honolulu-based journalist and former New York Times correspondent in Asia.