By Colin Packham

SYDNEY (Reuters) - Australian Prime Minister Malcolm Turnbull, whose leadership has been questioned after political setbacks, on Tuesday won a much-needed victory in parliament, with the passage of two controversial bills.

Australia's Senate, which the government does not control, passed a labor bill that it had previously blocked, triggering an election in July. The laws passed in a morning session, bring greater oversight of trade unions and employer bodies.

The parliament also passed a counter-terrorism bill in the evening. It extended police surveillance powers and cut to 14, from 16, the age at which terrorism suspects can be detained and face other restrictions.

Turnbull has seen his poll numbers hit their lowest since taking power in September 2015, and political commentators have questioned his future as prime minister, as confidence erodes in Australia's fourth leader in the last six years.

"The government called a double-dissolution election on this issue," said Haydon Manning, a political science professor at Flinders University in Adelaide, referring to the labor bill.

"To end the year without delivery on its set-piece reform would have been disastrous for the government."

Turnbull narrowly won the July 2 election after invoking rarely-used powers to dissolve both houses of parliament following the repeated blocking of the government's labor bill by the upper-house Senate.

But Turnbull has struggled to implement his agenda as his ruling conservative coalition is in the minority in the Senate, requiring him to win favor with many of the 11 independent senators to pass legislation.

Turnbull led negotiations on the labor bill with independent senators while in Peru this week attending the Asia-Pacific Economic Cooperation meeting, lawmakers told Reuters.

The government continues to trail the opposition Labor Party, a Newspoll on Tuesday showed.

Economic management, a traditional strong point for the conservative government, is now being called into question.

Deloitte Access Economic on Monday forecast the budget deficit to grow by A$24 billion ($17.69 billion) over the next four years - threatening Australia's AAA credit rating.

Turnbull now plans to turn his attention to another cornerstone piece of legislation aimed at creating a building industry watchdog. The bill was also twice rejected by the Senate in the lead-up to the July election.

That vote, in the final two weeks of the Senate's 2016 term, is expected to be tight, key independent Senator David Leyonhjelm told Reuters.

(Reporting by Colin Packham; Additional reporting by Tom Westbrook; Editing by Michael Perry and Clarence Fernandez)