By Linda Sieg
TOKYO (Reuters) - Japan took a step on Thursday towards enacting legislation for a policy shift that would allow troops to fight abroad for the first time since World War Two, part of the prime minister's agenda to loosen the limits of a pacifist constitution.
The security policy shift, which Abe says is vital to meet challenges such as a rising China, has sparked protests and sharply eroded his popular support.
Opponents argue it violates the constitution and fear it could ensnare Japan in U.S.-led conflicts.
Ruling Liberal Democratic Party member Masahisa Sato told NHK public TV that an upper house panel had approved the bills after a chaotic session, carried live on television, in which opposition lawmakers tried physically to block the vote, saying the vote was unacceptable.
Prime Minister Shinzo Abe's ruling bloc has a majority in the full upper house but opposition parties have pledged to use delaying tactics to try to keep the bills from passing before parliament adjourns on Sept. 27.
Thousands of demonstrators rallied near parliament on Wednesday chanting "Scrap the war bills" and "Abe resign" and they were gathering again on Thursday.
The protests were reminiscent of those that forced Abe's grandfather, Nobusuke Kinship, to resign 55 years ago after forcing a U.S.-Japan security treaty through parliament.
The revisions will end a decades-old ban on defending a friendly nation under attack, or collective self-defense, when Japan faces a "threat to its survival".
The measures expand the scope for logistics support for the militaries close ally the United States and other countries, and for participation in peace keeping.
The United States has welcomed Japan's shift, as have some Southeast Asian countries, worried by China's actions to bolster its claims in the disputed South China Sea.
China, where there is deep anger over Japan's brutal occupation before and during World War Two, has said the legislation would "complicate" regional security.
The revisions will still leave Japan constrained in overseas military operations by legal limits and a deeply rooted public anti-war mindset.
"The conditions imposed in the legislation and during the extended debate make it very clear that there will be real limits on what Japan can do and when," said Richard Samuels, director of the Japan program at Massachusetts Institute of Technology.
"It loosens to some degree constraints on some military behavior, but it ... does so under very strict conditions."
Abe has pledged to go ahead with the revisions despite polls showing the majority of voters want a better explanation of why they are needed.
(Reporting by Linda Sieg; Editing by Richard Pullin, Robert Birsel)