By Edmund Blair and Tamim Elyan
CAIRO (Reuters) - Hundreds of Egyptian Islamists protested in Cairo on Friday against what they said was a bid to bring back deposed president Hosni Mubarak's old guard after his last prime minister was allowed to stand in the presidential election.
But exposing divisions less than a month before an historic vote that marks the final step in a turbulent transition from army rule, youth movements and other activists who led the anti-Mubarak revolt last year did not join the demonstration.
The April 6 movement said it would not take part in protests that pressed for demands of a single group or party and the turnout was a fraction of the previous week when tens of thousands took to the streets.
Many youths who spurred on protests against Mubarak, putting national pride before religion, have struggled to turn street activism into an organized political force and fret about the dominance of Islamists in Egypt's new political arena.
Suspicions over the army's intentions were fuelled in the past week when Ahmed Shafiq, Mubarak's last prime minister who like every president for the past six decades has held a top military post, was first thrown out of the race and then reinstated hours before the final list was declared.
Thousands turned out in Egypt's second city of Alexandria and hundreds in other cities for the Islamist-led protest.
The Muslim Brotherhood, Egypt's biggest Islamist group that already dominates parliament, called for the demonstration to prevent "a delay in handing over power in June and to protest at the attempt to revive the corrupt former regime."
Generals who have ruled Egypt since Mubarak's overthrow last year have pledged to hand over power by July 1 to a new president. Thirteen candidates are running for the top job, whittled down from 23 in a tumultuous nomination process.
The four leading candidates can be broadly split between the Islamist camp and liberal-minded candidates who both served in office under Mubarak. The outcome is unpredictable with many voters undecided ahead of what will be Egypt's first real presidential vote in its history, analysts say.
The vote is set for May 23-24, with a run-off scheduled in June for the top two vote-getters. No candidate is expected to seal a first round win with more than 50 percent of the votes.
Confusion over who is eligible to run has highlighted the fragility of the democratic transition in the Arab world's most populous nation and raised questions about whether and to what extent the army will meddle in politics after its hand over.
Adding to uncertainty, the president is set to take office without clear powers because a row between Islamists and liberals over the make-up of an assembly to draw up a new constitution means it almost certainly won't be written in time.
"Down with military rule" and "Speak out and don't be afraid the (army) council must leave," protesters chanted, surrounded by vendors selling flags, trinkets, snacks and drinks in the square that was the centre for the uprising against Mubarak.
"The disqualification of Shafiq and his return raises concerns that there is some sort of arrangement," said Mohamed Abu Taleb, a 43-year-old accountant, protesting in Tahrir.
Though the army may welcome having one of its own again as president, it might lead to fresh street protests that could again bring the military back onto the streets and into the frontline of politics.
"Anything that would affect the handover would be really incendiary here. I think our sense is that the military are not at that point," said one Western diplomat.
Two other leading Islamists and Mubarak's spy chief were also among those excluded. They were not given a reprieve.
Shafiq's bid was briefly halted by a law drawn up by Islamists who swept up seats in a parliamentary election. They wanted to exclude candidates who were top officials in Mubarak's era. Shafiq challenged the constitutionality of the rule and was allowed to resume his campaign, while a court reviews the law.
Islamists are angry after their top contenders were thrown out. The Muslim Brotherhood has been forced to field a reserve candidate, Mohamed Mursi, after its first choice was ejected over a conviction in Mubarak's era when the group was banned.
Backers of a hard-line Salafi preacher are also angry that their candidate was thrown out of the race, when his deceased mother was found to have U.S. citizenship. Election criteria demand both parents hold only Egyptian nationality.
The backers of Hazem Salah Abu Ismail have stayed in the square since last week, accusing the committee charged with assessing candidates of targeting Islamists. Abu Ismail's supporters made up the biggest contingent in Tahrir on Friday.
Alongside Mursi and Shafiq, the other main contenders are Amr Moussa, the former head of the Arab League and one-time foreign minister, and Abdel Moneim Abol Fotouh, who was expelled from the Brotherhood when he announced a bid for the presidency at a time when the group said it would not field a candidate.
A poll in March, before the nomination turmoil, indicated Moussa was ahead. But his support has dipped from a few months ago. Mursi has the benefit of the Brotherhood's broad and disciplined network behind him, while Abol Fotouh has been building wider support, spanning liberals to Salafis.
Shafiq is expected to pick up votes from Egyptians who would like to see a more gradual transition in Egypt and see his military background as an asset in restoring order to a nation convulsed by protests and with an economy in tatters.
The Brotherhood has now more political representation than any time in its 84-year history. Seeking to capitalize on its unprecedented political gains, it has demanded to lead the formation of a new cabinet to replace the army-appointed one.
Rejecting parliament's latest call for him to quit, army-appointed Prime Minister Kamal al-Ganzouri said parliament had legislative powers but that the interim constitution did not give it powers to force out the government.
(Additional reporting by Yasmine Saleh; Writing by Edmund Blair)