CANBERRA - Australia's parliament delayed a final vote on a government carbon trade plan on Friday, missing a key deadline, throwing Prime Minister Kevin Rudd's climate change policy into doubt and raising the possibility of a snap election.

Rudd wanted the carbon scheme, central to his promise to cut emissions by between 5 and 25 percent, passed by Friday and ahead of December's global climate talks in Copenhagen, where he will play a key negotiating role.

But the upper house Senate failed to take a vote by the close of business on Friday, and will now return on Monday to continue debate on the package of 11 bills, with the government determined to push the bills through parliament.

We are committed to this scheme. I believe the Australian public are very strongly committed to action on climate change, Acting Prime Minister Julia Gillard told reporters.

If the proposed laws are defeated again in the Senate, after a first defeat in August, Rudd would have the option of calling a snap election in early 2010 and opinion polls suggest he would win with an increased majority.

The United States, the world's second largest greenhouse gas emitter, is eyeing developments in Australia as its lawmakers make slow progress on their own climate bill in the U.S. Senate.

Rudd had a deal with the opposition to pass the bills and needs seven opposition votes to pass the bills in the Senate.

But an open revolt by climate skeptics within the opposition has thrown the deal into doubt and on Friday prompted a leadership challenge as early as Monday against leader Malcolm Turnbull, who already survived one challenge on Wednesday.

A letter signed by 10 conservative lawmakers called for the fresh leadership vote on Monday, with former conservative minister Tony Abbott saying he will challenge for the job.

But the most likely candidate to replace Turnbull would be his treasury spokesman, Joe Hockey, who has publicly supported the carbon trade deal and who remains loyal to Turnbull.

A change of opposition leader could dramatically change the outlook for the carbon trade laws. A new leader could abandon the deal with the government, making the Senate numbers uncertain.

But if Turnbull holds the job, the laws could still pass through the Senate, although as many as 18 of his senators could defy their leader by voting against the bills.

The government would need seven of the remaining 19 opposition Senators to support the bills for them to pass.

The latest opinion polls show Rudd would easily win an election with an increased majority. The Reuters Poll Trend on Tuesday found Rudd had an almost 11 percentage point lead at 55.4 percent support compared to 44.6 percent for the opposition.

Turnbull ruled out standing down as leader and warned his party to support the laws or face a crushing electoral defeat.

We would be wiped out, Turnbull told Australian radio. the vast majority of Australians want to see action on climate change.

If this legislation is knocked back, Kevin Rudd will have no choice but to go to a double dissolution election. This is a fundamental plank in his platform.

(Editing by Nick Macfie)