By George Nishiyama

TOKYO, May 16 (Reuters) Japan should allow its military to defend U S forces in order to protect itself from North Korea's missiles, a two-time defence minister said today.

Fukushiro Nukaga, a defence expert in Prime Minister Shinzo Abe's ruling party, said Japan's self-imposed ban on collective self-defence -- defending an ally under attack -- should be loosened to strengthen Tokyo's security alliance with Washington.

The ban is based on a decades-old government interpretation of Japan's 1947 pacifist constitution.

''If U S bases in Guam and Hawaii come under attack by North Korean ballistic missiles and Japan has the ability to catch the missiles with our radar, should we just sit and watch?'' Nukaga told Reuters.

''While young American men are defending Japan, and their brothers and parents living in Hawaii are being attacked, would it be OK for us to just sit and watch?'' Under the bilateral security treaty, U S forces would defend Japan if it were attacked, but the opposite would not be possible because of the ban on collective self-defence, which is based on the U.S.-drafted 1947 constitution.

Article 9 of the charter renounces the right to wage war and forbids the maintenance of a military. Successive governments have interpreted the article as allowing a military solely for self-defence, but banning those forces from defending an ally.

Under that interpretation, while Japan has begun deploying a U S-made missile-defence system, Tokyo could not use it to shoot down missiles headed for U S territory.

Japan began considering the missile shield after North Korea fired a Taepodong ballistic missile in 1998 that flew over Japan.

Introduction of the system was speeded up after Pyongyang fired a barrage of missiles last July.

Nukaga said since U S bases in Guam and Hawaii play a key role in maintaining peace and security in Asia, any attack on them would be a threat to Japan's security, which would justify action by its military to defend the U S facilities.

NEIGHBOUR'S CONCERNS Prime Minister Abe last month set up a panel of experts to review the ban on collective self-defence, and the head of the panel has told Reuters it was leaning towards relaxing the ban.

The former defence chief also backs Abe's goal of rewriting the pacifist constitution and easing its limits on military actions overseas, but said restraints on what the Japanese military can do should be defined, perhaps under a separate law.

Abe's efforts to revise the charter have sparked concern in China and South Korea, which both suffered from Japan's wartime aggression, and critics at home have also said the move could result in Japan being dragged into war alongside the United States.

''I don't think people expect Japan to go all the way to the United States when it is being attacked there, and I don't think that is necessary,'' Nukaga said.

The ruling party lawmaker also said Japan should debate whether to arm itself with Tomahawk cruise missiles to enable it to strike North Korean ballistic missile bases.

Deploying Tomahawk missiles, made famous after U S forces fired them from navy ships to destroy inland Iraqi military facilities after Iraq invaded Kuwait in 1990, would be a break with Japan's policy against possessing offensive weapons.

''I'm not saying that we should deploy them. But we need to debate the security of our nation without any taboos.'' REUTERS ABM HT1535