Israel set for early vote as it ponders Iran challenge JERUSALEM (Reuters) - Israel's parliament convened on Monday to dissolve itself and set a September 4 election that opinion polls predict will renew Benjamin Netanyahu's leadership mandate as Israel confronts Iran's nuclear ambitions. The looming ballot has deepened doubts about the right-wing prime minister's threats to attack Iran and raised the question of whether his window of opportunity is now too narrow. "My intention is to form as wide a coalition as possible in order to bring about stability and lead Israel in the face of the great challenges still ahead of us," Netanyahu told his cabinet earlier in public remarks. The next national election was not due until October 2013, but new legislation that might force ultra-Orthodox Jews to serve in the military and an upcoming budget debate have threatened to unravel a governing coalition of religious and nationalist parties. Israeli leaders have insisted the election campaign would have no impact on their decision-making with regard to Iran, which includes the possibility of launching an Israeli strike against its nuclear installations. A Netanyahu victory two months before the U.S. election could give him leverage over Barack Obama on the Iranian and Palestinian issues while the president is still engaged in his own campaign and wary of alienating pro-Israel U.S. voters. "During this interim the new Israeli government will have absolute authority, while the U.S. administration will be impotent," said Ari Shavit, a columnist for the liberal Haaretz daily. "By bringing the election forward Netanyahu is defining the ideal time to attack Iran: September or October," he said in an analysis that was echoed by Israel's Channel Two TV. Netanyahu and Obama have had a thorny relationship and the Israeli leader has come under pressure from Washington not to take unilateral military action against Iranian facilities suspected of being part of a project to produce atomic weapons. Although Israeli leaders have hazarded war on the eve of ballots, taking on Iran would entail unprecedented military risks and would defy the United States still engaged in diplomatic efforts to resolve the nuclear dispute. Netanyahu may also be unwilling to risk his strong lead in the opinion polls by launching a risk-filled war and driving voters into bomb shelters. "There's no legal block to Israel attacking Iran now, but if it did so, the government would have to explain to the people why," said Yehuda Ben Meir, of Tel Aviv University's Institute for National Security Studies. I don't see that happening. On the subject of Iran, Netanyahu told a Likud convention on Sunday that he would "not ease the pressure until the threat is truly removed." A parliament dissolution vote is expected later in the day. Netanyahu and his government will remain in office until after the election and a new administration is sworn in. Political commentators have said Netanyahu is likely to end up with a similar coalition after the vote and had decided to pre-empt the ballot to capitalize on his strong poll showing. A system of proportional representation means there are 13 party groups in the present, 120-seat, single-chamber parliament. While opinion polls show strong support for Netanyahu's leadership, they also indicate that most Israelis either oppose an Israeli strike on Iran or would favor an attack only if it were carried out with U.S. agreement. The risks entailed in a strike on Iran's diffuse, well-protected nuclear facilities are so high and the Iranian response so uncertain that some analysts believe Netanyahu could only move once he has secured a new mandate from the people. Analysts have linked the urgency for an election to Israeli worries that Iran would within months fortify its uranium enrichment plants to the point of "immunity" from air strikes. But fractious Israeli politics, where prime ministers often spend weeks cobbling together coalitions, might also undermine the idea that Netanyahu would bounce immediately from the ballot box to the war room. September seems especially inauspicious for speedy party alliance-building given the long Jewish holidays at month's end. "There would be a caretaker government for at least a month, and then you're in October, when the operational window begins closing with the onset of winter," said Israeli defense analyst Alon Ben-David. He said an attack would probably have to be postponed to early 2013, if indeed it happens at all, given the big tactical challenge of reaching Iran's distant facilities. Editing by Angus MacSwan