* Islamists' opponents to rally on uprising anniversary
* Brotherhood decides to stay away from Tahrir Square
* Violence flares near Interior Ministry
By Tom Perry
CAIRO, Jan 25 (Reuters) - Egyptian President Mohamed Mursi's opponents head to Cairo's Tahrir Square on Friday to mark the anniversary of the uprising that ousted Hosni Mubarak with protests against the new head of state and his Islamist allies.
On the second anniversary of the uprising, Mursi's secular-minded rivals aim to revive the demands of a revolution that they say has been betrayed by the Muslim Brotherhood, the movement that propelled him to power in an election last year.
"I call on everyone to take part and go out to every place in Egypt to show that the revolution must be completed," Mohamed ElBaradei, a leading liberal, said in a statement.
"It will be against the Brotherhood," said Ahmed Maher, founder of the April 6 movement that helped mobilise the uprising against Mubarak through social media. "The goals of the revolution have not been realised yet," he told Reuters.
Inspired by Tunisia's uprising against President Zine al-Abidine Ben Ali, Egypt's revolution helped set off more revolts in Libya and Syria. But the sense of common purpose that united Egyptians at the time has given way to conflict that has grown only worse and last month triggered lethal street battles.
The anniversary will once again showcase the divide between the Islamists and their secular opponents. The Brotherhood has decided against mobilising in the street for the occasion, a decision that could reduce the likelihood of confrontation.
Mursi, in a speech marking the Prophet Mohammad's birthday, called on Egyptians to mark the anniversary "in a civilised, peaceful way that safeguards our nation, our institutions, our lives".
"The Brotherhood is very concerned about escalation, that's why they have tried to dial down their role on January 25," said Shadi Hamid director of research at the Brookings Doha Center.
"There may very well be the kinds of clashes that we've seen before, but I don't see anything major happening that is going to fundamentally change the political situation," he said.
Mursi faces discontent on multiple fronts.
His opponents say he and his group are seeking to dominate the post-Mubarak order. They accuse him of showing some of the autocratic impulses of the deposed leader by, for example, driving through a controversial new constitution last month.
The Brotherhood dismisses such criticism as unfair. It accuses its opponents of failing to respect the rules of the new democracy that put the Islamists in the driving seat by winning elections.
Six months into office, Mursi is also being held responsible for an economic crisis caused by two years of turmoil. The Egyptian pound has sunk to record lows against the dollar.
VIOLENCE FLARES NEAR TAHRIR
Other sources of friction abound. Activists are impatient for justice for the victims of political violence perpetrated over the last two years. Little has been done to reform brutal Mubarak-era security agencies. A spate of transport disasters on roads and railways neglected for years is feeding discontent.
Pointing to the potential for trouble, violence flared near Tahrir Square on Thursday when police clashed with several dozen youths who were trying to remove concrete barriers blocking a road to the nearby government offices.
Five members of the security forces were wounded by rocks and birdshot, the state news agency reported, and the smell of tear gas fired by the police hung over the square.
Some protesters began gathering in the square as night fell. "The people want to bring down the regime," said one banner, echoing the main chant of the revolt against Mubarak.
The parties that have called for Friday's protest list demands including a complete overhaul of the new, Islamist-tinged constitution that was fast-tracked into law by Mursi in December, a move that fuelled street violence.
Its critics say the constitution, which was approved in a popular referendum, offers inadequate protection for human rights, gives the president too many privileges and fails to curb the power of the military establishment.
Mursi's supporters say the criticism is unfair, that enacting the constitution quickly was crucial to restoring stability, and that the opposition is making the situation worse by perpetuating unrest.
With its eye firmly on forthcoming parliamentary elections, the Brotherhood is marking the anniversary with a big charity campaign. It aims to deliver medical aid to 1 million people, offer affordable basic foods, and renovate some 2,000 schools.
A strong turnout on Friday could also help the Brotherhood's opponents ahead of the elections. "There is a lot of power in this day and a real chance to use that to mobilise their supporters in the lead-up to the elections," Hamid said. (Additional reporting by Mohamed Abdellah; Editing by Jon Hemming)