* Reformists, centrists gained in parliamentary ballot

* Neither they nor conservatives won clear majority

* Pro-Rouhani parliament would speed economic reforms

* Early test will come in election for speaker



By Bozorgmehr Sharafedin and Sam Wilkin

DUBAI, May 12 (Reuters) - Iran's parliament reconvenes in late May with dozens of greenhorn lawmakers who will hold the key to accelerating reforms to boost foreign investment and trade - but whether they make or break the modernisation drive is hard to predict.

Elected in February, the 290-seat assembly replaces one dominated by hardliners suspicious of detente with the West and who curbed pragmatist President Hassan Rouhani's plans to liberalise the economy and raise lacklustre productivity.

Pro-Rouhani candidates raised their representation and 60 percent of MPs are first-timers.

Yet independent tallies suggest this will be the first parliament in more than 20 years without either a conservative or reformist majority, and the novices' allegiances may switch between Iran's many factions.

"On the one hand (this) is a positive sign of ...the possibility of fresh forces reaching parliament and new people gaining experience in lawmaking," said Jamileh Kadivar, a reformist former lawmaker now living in London.

"On the other ..., until the new representatives are able to gain the necessary experience, parliament could be outmaneuvered by other state bodies, or become susceptible to outside influence."

Even within the chamber the picture is unclear.

Iran does not have rigid party affiliations and some election candidates were backed by both camps, while deal-making ahead of the opening of parliament on May 27 could see independent MPs throw in their lot with one side or the other.

The contest to elect a speaker, one of parliament's first tasks, will be an early test.

If veteran reformist Mohammad Reza Aref can oust incumbent Ali Larijani, a conservative with broad appeal, that could herald a more actively pro-Rouhani chamber, with more power to push for his policies.

A centrist, Rouhani is under pressure to create jobs, boost the private sector, reduce graft and make the flagging economy more attractive to foreign investors - not least if he hopes to contest presidential elections in June 2017.



HOPE AND INEXPERIENCE

Both conservative and reformist camps worry the new faces may lack the clout to push -- or to block -- Rouhani's reforms and the experience to stay united in the face of setbacks.

Morale appears higher among reformists, despite the fact that their main parties remain banned after an uprising in 2009, with many prominent figures in jail or under house arrest.

The Guardian Council, a unelected 12-member clerical body, barred nearly all known reformist figures from standing in the elections. Their supporters then rallied around a slate of little-known candidates known as Hope List.

Hope Listers united during the campaign. Backed by Rouhani's moderate allies, former presidents Akbar Hashemi Rafsanjani and Mohammad Khatami, their candidates ended a decade of conservative dominance of parliament by ousting many hardliners.

But there is no guarantee reformists can sustain that harmony, and some analysts doubts the newcomers can challenge Iran's powerful religious establishment.

Rouhani is not free to steer economic policy, with the Guardian Council able to vet all laws, and Supreme Leader Ayatollah Ali Khamenei - who has in the past closed down parliamentary debates by decree - given the last word on important matters of state.

Ahmad Salamatian, a former lawmaker living in Paris, thinks the Hope List could fragment quickly if it loses momentum under such pressures, because it is held together only by popular support.

"The members of the Hope List ... can only remain united in the new parliament if they can maintain people's support by implementing tangible economic reforms, especially creating jobs," he said.

The conservatives, in contrast, suffer from an abundance of parties. They could not join forces during campaigning and their morale remains bruised after a heavy blow in the election - losing all 30 seats of the capital Tehran.



PICKING HIS BATTLES

Either way, without a majority Rouhani's government will have to pick its battles. Analysts say the president is likely to focus on pushing economic reform rather than social liberalisation.

That could bring a fresh set of problems, frustrating millions of young, well-educated Iranians who voted for him in 2013 hoping for more political and social freedoms.

For all the new faces, just 12 percent of incoming lawmakers are aged 40 or under, according to Interior Ministry data, whereas around 60 percent of Iranians are under 30.

And the record number of women elected to parliament still accounts for just six percent of the total, while they make up around 60 percent of university students.

"Having 18 women out of 289 elected members is not significant," said Kadivar, one of the few Iranian women to have made it there. (Editing by William Maclean and John Stonestreet) ((sam.wilkin@thomsonreuters.com; +971 4453 6873; Twitter @MrSamWilkin;))