FACTBOX - Australian PM back on knife-edge numbers

CANBERRA (Reuters) - Australian Prime Minister Julia Gillard's grip on power was weakened in January when a key independent lawmaker withdrew support for her minority government, cutting her majority back to just a single vote.

Gillard had strengthened her hold on power in late 2011 when an opposition lawmaker defected from his party to become parliament's speaker, effectively bolstering Gillard's majority to three with support of one Green and three independents.

But independent Andrew Wilkie withdrew his support for Gillard after she reneged on a deal to reform laws on slot-machine gambling, meaning Gillard is guaranteed 75 votes in the 150-seat House of Representatives.

The opposition can potentially muster only 74 votes in the lower house, if Wilkie and two conservative independents vote with the opposition.

Parliament's speaker does not vote on legislation, but does cast a deciding vote in the event of a tie.

Government is formed by the party which controls a majority in the 150-seat lower House of Representatives. But a bill must also pass the 76-seat upper house Senate to become law.

In the Senate, the government can pass bills with the support of the Greens, giving the government 40 of the 76 votes.

The Greens and independents who support Gillard have only committed to support the government on budget bills and no-confidence motions. They are free to vote as they choose on other matters, so numbers can vary on any bill or vote.

Following is a breakdown of seats by party.

HOUSE OF REPRESENTATIVES 150

Gillard's Labor Party 72

Greens 1

Independents 2

Total for government 75

Liberal/National opposition 70

Country Liberal 1

WA Nationals/independent 1

Independent 2

Total for opposition 74

Independent speaker 1

SENATE 76

Gillard's Labor Party 31

Greens 9

Unaligned independent 1

Democratic Labor Party (DLP) 1

Liberal/National opposition 34

(Reporting by James Grubel; Editing by Daniel Magnowski)