Japanese leaders for years have been edging their country away from its passive security stance. They agreed to join Western efforts in Iraq and Afghanistan by transporting cargo and refueling other navies’ ships, bought weapons that blurred the lines between defensive and offensive, and under Mr. Abe, doled out increasing military-related aid to neighbors who share Japan’s anxiety over China.

But the latest move differs from many of those actions in that it fundamentally changes the reading of the postwar Constitution and seems to take Japan further than ever from the renunciation of force as a way of settling disputes.

Mr. Abe, a longtime influential conservative, has tried in the past to win approval for a wholesale rewriting of the Constitution, part of his campaign to make Japan what he calls a more “normal” country that no longer hides its power out of shame for wartime transgressions. Lack of public support for those attempts, in part, cost him his job seven years ago, the last time he was prime minister.

Since then, the region has been transformed not only by China’s rise, but also a deterioration of American dominance that is leading several countries in the region to try to beef up their own military abilities.

Although Asia is not yet in an outright arms race, Richard J. Samuels, director of the Center for International Studies at the Massachusetts Institute of Technology, said Japan’s move showed that it and other countries were having to think more seriously about their own security than ever before.

“This is a recognition among these nations that U.S. capabilities are not what they were,” he said. “They are looking for a way to keep the U.S. in the neighborhood while also reaching out to each other in new ways.”