(Reuters) - Tens of thousands of Egyptians demanded on Friday that their military rulers stick to a pledge to hand over power by mid- year after a row over who can run in the presidential election raised doubts about the army´s commitment to democracy.

Two leading Islamist candidates, one representing the Muslim Brotherhood who was seen as the frontrunner, were among those disqualified this week from a vote that starts on May 23-24, drawing a storm of criticism from supporters and the candidates.

Khairat al-Shater, the Brotherhood´s former candidate, said his ejection showed the generals who have ruled since Hosni Mubarak was ousted last year had no serious intention of quitting. The movement is now fielding a reserve candidate.

"We are all here to protect the revolution and complete its demands," said Sayed Gad, 38, a pharmacist and Brotherhood member. He had joined a protest which attracted both Islamists and liberals to a packed Tahrir Square in central Cairo, although the two sides were not united on all their demands.

A council of generals, who stepped in 14 months ago after mass demonstrations in Tahrir and elsewhere had sapped Mubarak´s power, has led Egypt through a turbulent transition punctuated by spasms of violence and frequent protests against their handling of the move to democracy.

The army says it will stick to its timetable to hand power to a new president by July 1 and has promised to oversee a fair vote. But some remarks from military officials suggesting the army might also seek now to have a new constitution in place before that handover - an impossibly tight deadline for many - has added to popular worries about the military´s ambitions.

Western diplomats expect the timetable for transferring powers to hold but say the army which supplied Egypt´s presidents for six decades, including Mubarak, and which has built up sprawling business interests throughout that time, will remain an influential player behind the scenes for years.

OLD ORDER

"Down with military rule" and "The people want the execution of the marshal," some protesters chanted, a reference to Field Marshal Mohamed Hussein Tantawi, Mubarak´s defense minister for two decades who now leads the ruling military council.

Some demonstrators sheltered under awnings and umbrellas to shade them from the sun. Many waved Egyptian flags.

Although the protest passed off peacefully through the day, minor scuffles erupted between some Islamists and vendors in the square late into the night.

Witnesses said some protesters also threw stones and banged on the sides of buses carrying Brotherhood members as they tried to drive away, screaming "You sold the revolution".

Thousands also gathered in the second city Alexandria and turned out in some other cities. The hours after weekly prayers at mosques on Fridays are traditional times for protests.

Another candidate, Omar Suleiman, Mubarak´s former spy chief and briefly his vice-president, was also ejected from the race. His candidacy had raised fears the army wanted to roll back gains made since last year´s uprising, but there are still others in the race seen as vestiges of Mubarak´s old order.

"No to remnants. No to military rule," read one banner that carried pictures of Mubarak´s last prime minister Ahmed Shafiq, a former air force commander, and of Amr Moussa, a former foreign minister. They are both strong contenders, especially now that the Brotherhood´s Shater has been disqualified.

Responding on Twitter to Friday´s protest, Moussa said: "The exploitation of some of the square for narrow electoral goals and attacking some of the candidates is a negative phenomenon that should be followed up."

Rain rivals for Moussa and Shafiq will be Mohamed Mursi, the head of the Brotherhood´s political party who will have the weight of the group´s broad grass-roots network behind him, and Abdel Moneim Abol Fotouh, a moderate Islamist who was expelled from the Brotherhood when he announced his plan to run. At that time, the Brotherhood had said it would not field a candidate.

Mursi may have an edge because of the Brotherhood´s disciplined supporters behind him, but Moussa has strong name recognition as the former head of the Arab League. He won popular support for tough criticism of Israel. Abol Fotouh, who has been campaigning for months, could pick up voters now that more prominent Islamists have been pushed out the running.

Shafiq could be a choice for those Egyptians who are tired of protests and upheaval and view the military experience of the one- time air force commander positively, offering them hope that he can stabilize the nation.

But analysts say predicting an outcome is difficult when the race has no historical precedent in a nation convulsed by political turmoil after decades of post-colonial autocratic rule. Mubarak was elected by single candidate referendums or, in 2005, a multi-candidate vote that was widely viewed as rigged.

TENSIONS

Friday´s demonstration was the first in months to bring both Islamists and liberals together. Some of those gathered called for protesters to camp out in the square, as has happened in some previous protests since Mubarak was ousted.

"Those who left the square in difficult times must come back and not leave until the revolution´s demands are met," Kamal Helbawy, who quit the Brotherhood after its U-turn over a presidential bid, told protesters from one of the podiums.

Hundreds of soccer fans, or "ultras", gathered just off Tahrir. In February, clashes had erupted in that street after 74 supporters of the popular Al-Ahli soccer club were killed in stadium violence which fans blamed on bad policing. There was no immediate sign of a fresh flare-up, however, as fans chanted slogans against the military and praising those who had died.

Although broadly united in criticism of the army, the demands of Islamists and liberals are not fully aligned. Liberals also fret about the strength of political Islam after Islamists - notably the Brotherhood and smaller, harder line Salafi movement - swept a parliamentary vote in December.

Rows over who is eligible to run for Egypt´s first real presidential election in its history has added to tensions already running high over who should write the new constitution.

Liberals, as well as Christian and Muslim religious establishment figures, quit an assembly that was picked to draw up the new constitution because they said it was dominated by political Islamists and did not represent Egypt´s diversity.

The assembly, appointed by the new, Islamist-dominated parliament, has now been suspended.

But most demonstrators sought to play down any rivalries in Friday´s protest. "Hand in hand," protesters chanted, while one banner read: "Together against the continuation of army rule."

The April 6 youth group, which helped galvanize the anti-Mubarak demonstrations last year, had called for Friday´s protests in part to demand that new criteria be laid down to ensure a diverse make-up for the constituent assembly.

Also among the protesters were supporters of Hazem Salah Abu Ismail, an ultra-conservative Salafi candidate for the presidency who had built up a big popular following but who was also disqualified from the race because his mother had U.S. nationality, violating one of the rules for holding the office.

From a stage in Tahrir Square where his supporters had also gathered on Friday, people chanted over loudspeakers: "Islamic revolution! With our soul and blood, we sacrifice for Islam!" and "The Koran is the constitution!"

Hundreds of his supporters, among the last remaining in the square, vowed to stay overnight to express their anger at his disqualification.

(Additional reporting by Tamim Elyan and Ahmed Tolba; Writing by Edmund Blair; Editing by Alastair Macdonald and Alison Williams)(© Thomson Reuters 2012. 04/20/12)