The Greens look set to become the country's third political force in the parliamentary polls as environmental issues take on new importance in the world's most arid continent.

Opinion polls indicate the Greens, led by Senator Bob Brown, could do significantly better than the 5.0 percent of the vote they won at the last election in 2001, with some surveys pointing to a 9.0 percent score.

Brown, voting in his home state of Tasmania, took heart from the Nobel prize bestowed on Maathai for her work defending Africa's depleted forest cover.

"It's a great omen," Brown said.

Saving Tasmania's ancient eucalypt forests from commercial logging was the Greens' main election issue and they gained the backing of the main opposition Labor Party for the effort during the campaign.

Labor leader Mark Latham promised to spend hundreds of millions of dollars to reform the Tasmanian timber industry and restrict "old growth" logging if he wins the election.

Conservative Prime Minister John Howard, who opinion polls indicate will likely win reelection, also offered a less ambitious plan to restrict Tasmanian logging.

Australia's complex preferential voting system gives minor parties like the Greens disproportionate influence since they can often determine the outcome of polls in swing electorates by directing their votes to candidates from the major parties.

The Greens had one member in the outgoing 150-member House of Representatives and two Senators in 76-seat Senate.

If pre-election opinion polls hold true, the Greens are likely to gain some seats and replace the centrist Democrats as the third force in parliament behind Labor and Howard's Liberal-National coalition.

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