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By Sophie Walker

BAGHDAD, Oct 2 (Reuters) - Britain's Gordon Brown arrived in Baghdad on Tuesday on his first visit as prime minister to discuss when Iraqi forces can take responsibility for security in the southern province of Basra, a British official said.

Brown's trip comes before he makes a key statement on Iraq to parliament next week. British media has reported he may announce plans to trim the British force based in southern Basra province to 3,000 early next year from around 5,000.

As speculation grows in Britain that Brown is considering an early election, any signal British troops will be returning soon could be a further boost for a prime minister who is already enjoying a strong lead in the opinion polls.

"He's going to want to discuss the developing security situation in Basra and the prospect for Iraqis taking full responsibility, and the timescale for that," a British official told reporters travelling with Brown.

"This is part of the process of preparing and finalising the statement to parliament early next week."

About 500 British soldiers withdrew from a palace in the city of Basra to a vast airbase on its outskirts in early September. That pullout ended the British military presence in the city, where troops had been stationed since the U.S.-led invasion in 2003.

Brown will meet officials from the three main sects in Iraq: Shi'ite Prime Minister Nuri al-Maliki, Sunni Arab Vice President Tareq al-Hashemi and Deputy Prime Minister Barham Salih, a Kurd. He will also hold a news conference at 12.30 p.m. (0930 GMT).

The decision by Brown's predecessor Tony Blair to join the invasion of Iraq in 2003 was deeply unpopular in Britain and his ruling Labour Party, and ultimately led to him being hounded from power after a decade in office.

Since taking over in June, Brown has sought to draw a line under Blair's rule and there has been growing speculation he wants to pull more troops from Iraq, perhaps as a precursor to calling a snap general election.

Foreign Secretary David Miliband acknowledged last week that Britain's role in Iraq had scarred the government and divided the country and said the party now had to focus on the future.

Brown does not have to call an election until 2010. However his solid lead over the main opposition Conservative Party has boosted talk among political commentators that he may call a national vote to win a popular mandate.

Some political analysts still say he is unlikely to take the risk as he could end up with either a smaller majority, or out of office all together after waiting so long for the top job.

Economic development will be a big theme in Brown's visit to Iraq and the prime minister will want an update on the process of political reconciliation, the British official said.

Feuding between Iraq's political camps has hamstrung the government and delayed progress on key reforms Washington wants.

Officials stress Britain has no fixed timetable for withdrawing troops from Iraq but a rough schedule for cutting numbers is expected soon following talks with Washington.

The focus will then be on transferring responsibility for Basra province to Iraqi authorities by the end of the year, completing the handover of power in all four southern provinces for which Britain was once responsible.

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