* Muslim Brotherhood to contest half of parliament seats
* Alliance with other groups aims to allay liberal concerns
By Yasmine Saleh
CAIRO, June 22 (Reuters) - Egypt's Muslim Brotherhood is exploring an alliance with 17 liberal and other parties that could lead to electoral cooperation, in an apparent move to allay liberal concerns about the Islamist group's goals.
The Brotherhood, Egypt's most organised political force, is widely seen as best prepared for the September parliamentary election as many secular parties struggle to get ready for the first free vote since President Hosni Mubarak's overthrow.
The Brotherhood, officially banned but semi-tolerated under Mubarak, has said it will contest half of parliament's seats, seeking to capitalise on the grass roots networks it has nurtured during decades of medical, social and charity work.
Activists who put national pride before faith in the uprising against Mubarak fear the Brotherhood will dominate politics and seek to impose strict Islamic rules on Egypt.
A statement posted on the Brotherhood's website said it had agreed with other parties "on ways that could lead to a joint election list to include representatives from all members of the alliance that would gain the trust of the Egyptian masses".
Yassin Tageldin, deputy chairman of the liberal Wafd party, said such an electoral deal could be struck if talk of a law forcing candidates to form lists materialised.
"The Brotherhood wants to appear that it favours engaging in a dialogue ... and that it goes along with liberals," said Emad Gad of the al-Ahram Centre for Political and Strategic Studies.
"But I do not it see it as a real alliance, they have not agreed on any details," he added.
Wafd, a party that dates from the early 20th century, was one of the few allowed to operate in Mubarak's time. Many requests to form parties were rejected by a committee that was led by the secretary-general of Mubarak's ruling party.
Many liberal and secular politicians are now struggling to organise parties to compete with the Brotherhood, which has formed the Freedom and Justice party, and other Islamist groups.
Some liberal groups criticised the nascent alliance.
"We have been witnessing with a mixture of surprise and wonder the Freedom and Justice party and Wafd party calls to form an electoral alliance," said a statement from Al Masreyeen Al Ahrar (Free Egyptians).
The party, led by telecoms tycoon Naguib Sawiris, a Christian, added that it "still has concerns about the direction of the Islamic political currents".
Wafd's Tageldin dismissed such worries, saying: "The Brotherhood has agreed to engage in the political game and approve the concept of having a civil state and to work with others to achieve the goals of the revolution."
Analysts say the Brotherhood could win up to 20 percent of seats, which would match its best performance under Mubarak when it thrived on protest votes even though elections were routinely rigged against it. Others say it could get many more seats.
Wary of Islamist strengths, some more liberal groups have mounted a "Constitution First" campaign demanding that the September poll is delayed until the constitution is re-written.
They say this would allow more groups time to organise and ensure that it was not left to an Islamist-dominated parliament to draw up a new constitution after the election.
Some liberals fear that, if in left in charge, Islamists could set restrictions on women, ban alcohol which would hurt tourism and add to tensions with Egypt's Christian minority. (Editing by Edmund Blair and Alistair Lyon)