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CANBERRA, Australia (AP) — Australians choose Saturday whether they will cut down their first woman prime minister after only two months in power and return to conservative rule in a cliffhanger election that threatens the survival of a first-term center-left government.

Voters face an unusual choice between two relative unknowns: a prime minister whom they didn't elect and a fledgling opposition leader who barely gained the endorsement of his own party eight months ago.

Polling booths opened at 8 a.m. Saturday (2200 Friday GMT) in eastern Australia and would close 10 hours later. Time zones meant the west coast would continue voting for another two hours.

Opinion polls point to a close contest between the ruling center-left Labor Party and the conservative Liberal Party-led coalition that has mostly been in government since World War II. Large regional variations in voter swings evident in most polls complicate forecasts of which side will win a majority in the 150-seat House of Representatives where parties form governments.

Both Prime Minister Julia Gillard and Liberal leader Tony Abbott ended their five-week election campaigns on Friday by warning voters their opponent's untested leadership threatened the prosperity of Australia's 1.3 trillion Australian dollar ($1.2 trillion) economy.

Australia scraped through the global financial crisis without falling into recession, although Abbott has argued the government spent too much to keep a sluggish economy growing.

Gillard, a Welsh-born child immigrant with a working-class accent, stunned Australians when she launched a sudden challenge to Prime Minister Kevin Rudd's leadership on June 24 as the government was rattled by a series of poor opinion polls.

The decision by Labor power-brokers to support Gillard — a cheerfully charismatic and sharp-witted 48-year-old former lawyer who is widely regarded as a better communicator than Rudd, a wonkish and temperamental former diplomat — cost the party the traditional advantage for the incumbent of going to elections with a known quantity as leader.

Gillard on Friday told reporters in Sydney, where voters were turning toward the conservatives, that Labor could lose its entire eight-seat majority. Labor won 83 seats at the last election in 2007.

"What we know from the opinion polls is this, that there is a real risk that Mr. Abbott could be prime minister on Sunday," she said.

Australians have not dumped a first-term government since 1931 when a Labor administration paid the ultimate price for the Great Depression. But Abbott, a 52-year-old former Roman Catholic seminarian whose socially conservative views alienate many women voters, said Gillard's government does not deserve a second chance because it dumped the elected prime minister.

Abbott said Rudd was made a scapegoat for the government's wasteful economic stimulus spending that will next year see debt peak at AU$94 billion ($83 billion) — or 6 percent of gross domestic product.

"Elections are an opportunity for the people to pass judgment on the competence or otherwise of the government," Abbott said. "Just as I expect the current government to be judged."

Gillard acknowledges mistakes, including a bungled AU$2.5 billion program to provide free ceiling insulation for homes, which was scrapped after four laborers died while installing it and scores of house fires were blamed on poor workmanship.

A government-commissioned report found numerous examples of poor value for the money in a AU$16 billion program to provide every school in Australia with a new building.

Abbott is his party's third choice as leader since Prime Minister John Howard led it to defeat in 2007. Abbott beat his predecessor by a single vote in December last year in a party ballot that hinged on the Liberals' policy to tax major polluters for every ton of carbon gas they emit. Abbott doubts climate change science and opposes any carbon tax.

He has long had a reputation as a gaffe-prone fitness enthusiast who is often lampooned in the media over the many images of him clad in Lycra cycling and swimming wear.

Government lawmakers dubbed him "Phony Tony" after he explained a policy backflip during a television interview in May. But analysts agree his relatively mistake-free campaign and his party's strong opinion polling attest to a more disciplined approach.