TOKYO (Reuters) - Prime Minister Shinzo Abe began the toughest battle of his political life in a parliament session that opened on Monday after staking his job on extending Japan's naval mission in support of U.S.-led operations in Afghanistan.

"The military personnel who are silently doing service on the scorching Indian Ocean embody Japan's international contribution sought by the world," Abe said in a policy speech to parliament.

"Can we really pull out now and abandon our responsibility to the international community?"

Opposition parties, which won control of parliament's upper house in a July election, are against the mission to refuel coalition ships in the Indian Ocean and could delay enactment of a bill to extend it beyond its November 1 expiry.

Abe's policy speech, generally politely received in the lower house, prompted loud jeering and heckling in the upper chamber.

Failure to extend the mission could sour Tokyo's ties with Washington, which has made clear it sees the activities as vital.

Abe told a news conference on Sunday he would not "cling to his duties" if the mission were to end, prompting some to suggest the weakened leader was seeking an honorable excuse to quit.

Financial markets are more worried about a decline on Wall Street and a jump in the yen against the dollar, but concerns about politics remain, especially as figures on Monday showed Japan's economy contracted in the second quarter.

Just when a showdown over the mission would come is hard to predict. The opposition could vote down enabling legislation quickly and send the bill back to the lower house, where the ruling camp could enact it with its two-thirds majority.

But few expect the opposition to be so obliging.

The government could submit a new bill and try to pass it by extending parliament beyond November 10, when the current session is set to end, or in a regular session from next January, although the delay would require a halt in Japan's refueling operations.

A brief suspension, the top government spokesman said, need not trigger Abe's resignation. "In music, there are times when there is a pause and then the music continues. That is still considered one single song," Kyodo news agency quoted Chief Cabinet Secretary Kaoru Yosano as telling a news conference.

HONOURABLE RETREAT?

Abe, who took office a year ago vowing to boost Japan's global security profile, has already been weakened by scandals and gaffes by ministers that contributed to a drubbing for his Liberal Democratic Party (LDP) in the election and will provide fodder for opposition grilling in parliament in the coming weeks.

Some think Abe may now be setting the stage to resign with his head held high after a battle over diplomacy that paints the main opposition Democratic Party of Japan (DPJ) as irresponsible.

"It's a time-honored Japanese tradition to prepare for an honorable exit," said Koichi Nakano, a political science professor at Tokyo's Sophia University.

"The idea may be to make it easier to extend the support activities by putting his job at stake, but a change in the Democratic Party's stance remains very doubtful," Nakano said.

Abe's ally Taro Aso, the hawkish secretary-general of the LDP, now appears the frontrunner to succeed if the premier quits.

Others said Abe was trying to increase pressure on Democratic Party leader Ichiro Ozawa to compromise while avoiding a snap election for parliament's powerful lower house that the ruling camp could well lose.

"The DPJ strategy is to force a dissolution of the lower house. It could happen accidentally," said Toru Umemoto, a currency strategist who analyses politics for Barclays Capital.

"The Liberal Democratic Party's is the opposite -- to avoid a dissolution of parliament before the end of the year."

Abe reshuffled his cabinet late last month, only to see one of his new line-up resign a week later.

Farm minister Takehiko Endo became the fifth to exit an Abe cabinet, four through resignation and one by committing suicide, when he quit over illegal deals at a farmers' group he headed.

A spate of other ministers and LDP officials have also admitted to discrepancies in their political funding records, helping to erode a boost in support that Abe had received after tapping veteran lawmakers for his new cabinet.

TV Asahi said on Monday support for the cabinet slipped to 31.8 from 36.6 percent in a September 1-2 survey. About 60 percent of respondents said Abe should quit by the year-end if not sooner.

(Additional reporting by George Nishiyama, Rika Otsuka and Isabel Reynolds)