* Army tries to retake Tikrit from insurgents
* Parliament votes on new speaker
* Maliki seeking third term as prime minister
By Isra' al-Rubei'i and Ahmed Rasheed
BAGHDAD, July 15 (Reuters) - Iraq's army and Shi'ite militia forces launched an assault on Tuesday to retake the city of Tikrit from Islamist militants as parliamentarians in Baghdad prepared to vote for a new speaker, a possible step towards breaking months of political deadlock.
The Defence Ministry said ground troops backed by air support began their offensive at dawn against insurgents, led by the al Qaeda offshoot the Islamic State, who have held Tikrit since mid-June.
If the army and its militia allies retake Tikrit, hometown of Saddam Hussein, it would be the first insurgent-held city to switch back to government control since Iraq's latest crisis erupted last month.
The offensive took place as Iraq's deeply divided parliament met for a third session aimed at forming a new government to tackle the insurgency, three months after the country held a parliamentary election.
Shi'ite Prime Minister Nuri al-Maliki, whose State of Law group is the largest individual bloc in parliament, is seeking a third term but faces opposition from Sunnis and Kurds who say he has ruled for the Shi'ite majority at the expense of minority communities. Even rival Shi'ite parties want to unseat him.
Acting speaker Mehdi al-Hafidh called on deputies to cast their votes for a new speaker, the first of three leadership posts which need to be decided. Moderate Sunni Islamist politician Salim Jabouri is front runner for the speaker's role.
The other posts to be decided are the presidency followed by the prime minister, but it was not immediately clear whether the planned vote for a new speaker was part of a wider deal to break the prolonged deadlock.
The political impasse has been given added urgency by the Islamist-led insurgency which swept through Sunni provinces of northern Iraq last month, encouraging Maliki's opponents to try to force his departure.
ARMY AND MILITIA
Sunni grievances against Maliki have helped the insurgency win support in the predominantly Sunni provinces to the north and west of Baghdad where the Islamic State and other militant groups have taken over.
Government forces retreated when Sunni insurgents overran Mosul on June 10 and swept south to seize Tikrit, 100 miles (160 km) north of Baghdad, two days later. The city is a stronghold of Saddam loyalists and ex-army officers who joined forces with the Islamic State assault.
An officer taking part in Tuesday's attack said uniformed volunteer fighters and militia forces, including the Shi'ite Asa'ib Ahl al-Haq, were fighting alongside the army, but following orders from their own militia and volunteer commanders.
The assault was launched from the village of Awja, some 8 km (5 miles) south of the city. The army retook Awja, the birthplace of Saddam, on the night of July 3, and has been trying to push north since.
The initial fighting on Tuesday focused around the Shishin district of south Tikrit, the officer and another soldier said, adding that the army was also heading towards Saddam's former presidential palace compounds, where Islamic State fighters had held captives and run their Islamic court trials.
Soldiers were also fighting to take Tikrit hospital which lies on a strategic area of high ground in the city.
Across the Tigris River to the east, the army landed paratroopers in Albu Ajeel where Iraqiya state television said some of the insurgents had fled. One army officer in the fighting said they were surprised the resistance they experienced was less fierce than expected. (Additional reporting by a correspondent in Salahuddin province and by Maggie Fick in Baghdad; Writing by Dominic Evans; editing by Janet McBride)