SYDNEY, Australia (CNN) -- Veteran Prime Minister John Howard was fighting for political survival Saturday, as Australians went to the polls in a federal election that could sweep a center-left opposition leader into power.
Australian Prime Minister John Howard is facing the prospect of a defeat in elections.
Howard -- the second longest-serving leader in Australian history -- found himself trailing in his quest for a fifth term despite a strong economy and record low levels of unemployment.
Voter fatigue with Howard's long tenure appeared to be weighing on his support, along with unpopular cuts to worker entitlements and a record drought that put climate change front and center as an issue in the race.
Pre-election polls showed Kevin Rudd's Labor Party leading Howard's center-right Liberal-National coalition -- which has governed Australia since 1996 -- although the race appeared to tighten in the closing days.
Rudd, 50, an ardent critic of the Iraq war, has said he would start a phased withdrawal of Australian forces from the country if Labor won the vote.
After meeting with President Bush in September, however, the Labor leader said Australia would continue its military presence in Afghanistan, and he expressed support for the Australian-American alliance.
Howard, 68, was a staunch supporter of Bush's decision to go to war.
Despite Rudd's and Howard's differences over Iraq, the conflict did not play a dominant role in the campaign. Howard had handily won re-election in 2004 in spite of public opposition to his Iraq policy.
Both men agreed the election will be close.
"It's not over yet," Howard said this week, telling supporters Wednesday the election was still winnable for his coalition.
"Whoever wins this election on Saturday will win by a nose," Rudd told the National Press Club in the Australian capital Canberra on Wednesday. Watch why climate change may play a role in the election »
Going to the polls is legally required for Australia's 13.6 million enrolled voters, who can be fined if they don't cast a ballot. The unusual compulsory system resulted in a turnout of more than 94 percent in the last election.
Voters on Saturday were picking all 150 members of the lower chamber of Parliament, the House of Representatives. Labor needs to make a net gain of 16 seats in order to win a majority and claim the prime minister's post.
Forty of the 76 seats in the Senate were also up for grabs, with Howard's coalition trying to hang on to a slim majority in the upper chamber.
While the Senate election has no bearing on who becomes prime minister, the outcome could have an effect on the ability of the winning party to get its legislative program through Parliament.
Rudd, who was a diplomat in Beijing and speaks fluent Mandarin Chinese, is expected to continue his party's long-standing policy of focusing more attention on relationships with its Asian neighbors.
Polls opened at 8 a.m. across Australia's three time zones. The last polls were set to close in Western Australia at 6 p.m. (4 a.m. ET). E-mail to a friend
CNN's Hugh Riminton contributed to this report.