The United States missile defence chief is in Tokyo for talks on forging closer ties on ballistic missile defences.
Japanese officials said the director of the Pentagon's Missile Defence Agency, General Ronald Kadish, urged Japan to consider using an American programme including both ship-based and ground-to-air missiles.
The Japanese Defence Minister, Shigeru Ishiba, is reported as saying that his government needs further debate before making a decision.
Correspondents say ballistic missile defence has been a top priority for Japan since North Korea fired a rocket into the Pacific Ocean in l998.
Further impetus has been added by Pyongyang's admission that it is seeking to develop nuclear weapons as a deterrent to what it calls American aggression.
From the newsroom of the BBC World Service