TOKYO, (Reuters) - American Airlines said that it, private equity firm TPG and Oneworld alliance partners could increase their $1.1 billion investment offer to Japan Airlines, depending on the struggling carrier's restructuring plan.

"Conceivably there could be a bigger investment made by the Oneworld/TPG/American group depending on the circumstances that have to be worked out with the government and with JAL," American Airlines CEO Gerard Arpey told a news conference in Tokyo.

JAL is weighing rival financial aid packages from American and Delta Air Lines as part of a revival effort that hinges upon a capital injection from a turnaround fund backed by the Japanese government and debt forgiveness from its banks.

Asia's largest carrier by revenue appeared to increase the possibility it would get a state bailout with an announcement on Tuesday that most of its retirees were willing to accept cuts to their pension payouts.

Shares of JAL, which have lost more than half their value this year, jumped three percent on the news. Reducing its $3.7 billion pension shortfall is a prerequisite to receiving a bailout from the Enterprise Turnaround Initiative Corporation of Japan (ETIC), the state-backed fund set to decide on whether to support the airline as early as next month.

Arpey, who is also CEO of American's parent AMR Corp, said its investment into JAL would have to be coordinated with the support of the government. He did not answer directly a question on whether American Airlines and its partners would be willing to invest before the ETIC makes its decision.

If the ETIC decides not to support JAL the airline would likely be restructured in bankruptcy court.

"It is part of the overall restructuring that will involve JAL, the government, us and TPG. So I think it all has to happen in concert," Arpey said, following a meeting with Transport Minister Seiji Maehara.

Executives at Delta, which along with SkyTeam alliance members has offered a $1 billion financial aid package to JAL including a $500 million equity investment, met with Maehara last week to press their case for wooing JAL away from Oneworld.