FACTBOX-How an Australian election works

SYDNEY, July 16 (Reuters) - Australian Prime Minister Julia Gillard is likely to call an election on Saturday for August 28, public broadcaster ABC reported on Friday, quoting sources from the ruling Labor party.

The ABC said Gillard would visit Governor-General Quentin Bryce in Canberra on Saturday morning to seek permission to call an election. [ID:nSGE66F02P]

Gillard’s Labor government is narrowly ahead in opinion polls but is struggling to sell sensitive policies on the economy, resources, climate and asylum seekers.

Below are facts on Australian politics:

* Australia has a bi-cameral parliament, based on Britain’s Westminster system. Parliament has two chambers, the lower House of Representatives and the upper house Senate.

* The government is formed by the party with the majority of lawmakers in the House of Representatives.

* The 2010 Australian election is a full lower house and a half Senate election.

* There are 150 members of the House of Representatives. They will be elected for three years, although the government can call elections earlier. The house of Representatives uses a preferential voting system.

* Labor currently holds 83 seats in the House of Representatives, Liberal holds 54, Nationals hold 9 and Independents hold 4 seats.

* PM Julia Gillard’s Labor party will need to win 76 seats to hold a clear majority in the upcoming elections.

* Voting is compulsory for Australians over the age of 18.

* House of Representatives seats are based on population, leading to vast differences in size. The inner Sydney seat of Wentworth covers 30 sq km, while the Western Australian seat of Durack covers 1.6 million sq km.

* There are 12 Senators for each of the 6 states and two for Australian Capital Territory and the Northern Territory respectively.

* To win a Senate seat, a candidate must win a proportional representation which means a candidate needs to gain about 14 percent of the vote across their state, while territory senators need 33 percent to be elected. The system helps minor parties and independent candidates.

* There are 150 electorates, each seat has about 92,000 voters.

* The latest Reuters Poll Trend released on July 2, suggests Gillard has a good chance of a narrow victory. The Reuters Poll Trend shows Labor with a narrow 3.2 point lead on a two-party basis with 51.6 percent support, compared to 48.4 percent for the conservative opposition. (Reporting by Amy Pyett; Editing by Sugita Katyal)