Within a couple of hours of landing in Japan on Friday, President Obama walked into a political minefield by implicitly promising someday to visit Hiroshima and Nagasaki, the targets of American atomic bombs in 1945.

After meeting with Prime Minister Yukio Hatoyama, Obama was asked by a Japanese reporter in an evening press conference whether he would go to Hiroshima and Nagasaki, where no U.S. president has ever been. "What is your understanding of the historical meaning of the A-bombing in Hiroshima and Nagasaki?" the Japanese asked. "Do you think that it was the right decision?"

"I certainly would be honored," the president replied. "It would be meaningful for me to visit those two cities in the future."

The Japanese reporter persisted, asking again whether the U.S. was right in dropping the atomic bombs. Obama slid off the question, turning to the charged issue of North Korea's efforts to acquire nuclear weapons.

A presidential journey to the only cities to have experienced a nuclear assault would underscore Obama's intent to rid the world of nuclear arms. If not handled with sensitivity, however, the visit could trigger emotional outbursts from Japanese victims of the bombings and from Japanese who experience a "nuclear allergy."

Many Japanese, particularly left-wing organizations, would most likely demand that the United States apologize for dropping the bombs, which would stir up rancor in America. That would call into question the judgment of President Harry Truman, who made the decision to drop the bombs. In turn, that would put President Obama in a politically difficult position.

Among Americans, veterans of World War II, especially survivors of Japan's surprise attack on the U.S. naval base at Pearl Harbor on Dec. 7, 1941, would be vigilant for any sign of remorse for an action that many believe ended World War II with Japan's surrender, sparing the lives of tens of thousands of Americans poised to invade Japan.

In addition, many American private citizens, whether they lived through the war or not, would insist that a U.S. presidential visit to Hiroshima and Nagasaki be preceded by the visit of a Japanese prime minister to Pearl Harbor. That has not happened so far.

In April, the president set a lofty goal, saying in Prague that "as the only nuclear power to have used a nuclear weapon, the United States has a moral responsibility to act." Obama continued: "Today, I state clearly and with conviction America's commitment to seek the peace and security of a world without nuclear weapons."

The president followed up in Tokyo yesterday with a wide-ranging address on American policy in Asia that included a passage on nuclear arms. Americans and Japanese, the president said, must "redouble our efforts to meet a threat to our security that is the legacy of the 20th century — the danger posed by nuclear weapons."

"Indeed," Obama said, "Japan serves as an example to the world that true peace and power can be achieved by taking this path. For decades, Japan has enjoyed the benefits of peaceful nuclear energy, while rejecting nuclear arms development — and by any measure, this has increased Japan's security, and enhanced its position."

The president, however, emphasized: "Let me be clear: so long as these weapons exist, the United States will maintain a strong and effective nuclear deterrent that guarantees the defense of our allies — including South Korea and Japan." Leaders in both nations have expressed concern that the United States would withdraw that extended deterrence, also known as the "nuclear umbrella."

From Japan, Obama's itinerary took him to Singapore for meetings with leaders of the Asia Pacific Economic Cooperation forum and of the Association of Southeast Asia Nations. He then goes to China and South Korea.