By Linda Sieg and Nobuhiro Kubo
TOKYO (Reuters) - Japan and ally the United States can start making plans for a possible conflict with China after the expected enactment of defense legislation this week, but Japan will not be sending troops to back up U.S.-led operations against Islamic State.
Those two scenarios show both how far Japan will have come in loosening the constraints of its pacifist constitution on its military and how far it will remain from being a "normal nation", unconstrained in overseas military operations by legal limits and a deeply rooted public anti-war mindset.
Some in Japan worry that the gap between what Japan can or will do and what the United States hopes for could cause friction with Washington if a failure to meet overblown expectations means it becomes disillusioned with its Asian partner.
"With these legal changes, we will be able to do almost everything the United States has asked. There is almost nothing we cannot do when it comes to things like providing ammunition and rear-guard support," a Japanese naval officer told Reuters.
"But what America really wants is for Japan to fight in the war against terrorism," he added. "If U.S. public opinion rises against Japan, this will be a problem."
Despite public protests and surveys showing a majority of voters object, parliament's upper house is expected as early as this week to enact defense bills Prime Minister Shinzo Abe has called "the first of its kind and a sweeping" reform.
The changes include an end to a decades-old ban on defending a friendly nation under attack, or collective self-defense, when Japan faces a "threat to its survival".
They also expand scope for logistics support for U.S. and other countries' militaries and participation in multinational peacekeeping operations.
The United States has welcomed the shift, while China, where anger over Japan's brutal occupation before and during World War Two is still deep, has said the legislation would "complicate" regional security.
Domestic critics say the changes violate the constitution and open the door to entanglement in U.S.-led conflicts.
Abe, in response, has in principle ruled out sending troops to fight in foreign territory and said Japan would not even provide logistical support for U.S-led operations against Islamic State.
"Japan is not going to be like Australia, the U.K. or Germany in that those countries have been providing all sorts of human assets to war zones, Afghanistan, Iraq. That is not going to be a thing that Japan can do," a Japanese government source told Reuters.
STILL NOT "NORMAL"
The changes leave Japan still short of being a "normal nation" by global security standards. Collective self-defense, for example, will only be exercised if three conditions are met including a "threat to Japan's survival".
"It is a big step by Japanese standards but not huge by major power standards," said Narushige Michishita, Japan scholar at the Woodrow Wilson International Center for Scholars.
That said, closer integration with U.S. forces in particular opens the door not only to expand peace-time patrols and exercises but also to start join planning for conflict.
"It will enhance deterrence and integrate Japan much more closely not just with the United States, but with Australia, the Philippines and other U.S. allies," said Michael Green, Japan chair at the Center for Strategic and International Studies
"Japan can be integrated in the use of force - not Japan doing offensive missions, but supporting the United States in an emergency that is a threat to Japan's interests and survival."
Michishita said the legislation would allow Japan and the United States to begin planning to defend the "first island chain", an arc of islands enclosing China's coastal waters from the Kuril Islands southward through the Japanese archipelago, Taiwan and the northern Philippines to Borneo.
"From the military operations perspective, this is most important," said Michishita, a former defense official.
Still, some in Japan worry a perception gap with the United States over what Japan can or will do could lead to damaging friction.
"There are experts in the United States who have the misconception that Japan will be able to exercise collective self-defense based on international law and equivalent to what the United States can do," said former defense minister Satoshi Morimoto. "Japan is going to have to make a lot of effort in this area (to avoid friction)."
(Writing by Linda Sieg)