* Salafist preacher Borhami calls for answers on Rabaa killing
* Borhami says Sisi "has problems" among Islamists in general
* Analyst says Nour would find it hard to back Sisi publicly
By Sameh Bardisi
ALEXANDRIA, Egypt, Jan 23 (Reuters) - Egypt's second biggest Islamist faction may have rallied behind a new army-backed constitution passed in a referendum last week, but its support for a presidential bid by military chief General Abdel Fattah al-Sisi appears less certain.
A leading cleric in the Dawa Salafiya, the Islamist movement that spawned the Nour Party, indicated in an interview that support for a Sisi bid hinged on a fuller government explanation of last year's mass killing of supporters of deposed president Mohamed Mursi, the Muslim Brotherhood politician overthrown in July.
Nour Party support has provided a degree of Islamist approval for the course charted by the army since it removed the Muslim Brotherhood's Mohamed Mursi from the presidency following mass protests against his rule.
Were it to decide against endorsing Sisi for president in an election that he is widely expected to contest and win, it risks exposing more starkly the divide between the Islamist movement and the Egyptians who mobilised to remove Mursi.
"General Sisi has problems among many in the Islamic movement: it is the case of Rabaa and the bloodshed that followed," said Yasser Borhami, deputy head of the Dawa Salafiya, asked if the Nour would back Sisi for the presidency.
Rabaa al-Adawiya is the mosque in northeast Cairo where security forces killed hundreds of people on Aug. 14 while breaking up a sit-in by Muslim Brotherhood supporters.
The government had called the sit-in a threat to national security, and says the security forces came under fire.
"This is fundamental to the grass roots of the party. What happened needs clarification, I mean the way the sit-in was disbanded. What were the orders given to the forces? There was a lot of killing, and this should be clarified to the public," Borhami told Reuters in an interview at his home in Alexandria.
INQUIRY INTO VIOLENCE
The government established a fact-finding committee that is investigating all violence since June 30, the day of mass anti-Mursi protests that led to his removal by the army. Established on Jan. 6, it has six months to complete its work.
The dispersal of the Cairo sit-in was followed by the bloodiest bout of internal strife in Egypt's modern history, including an ongoing series of bomb attacks and shootings targeting the security forces: five policemen were shot dead south of Cairo on Thursday.
Sisi is widely expected to announce his candidacy for the presidency imminently, and the election could happen as soon as March or April. He enjoys wide backing among Egyptians who supported Mursi's removal one year into a divisive presidential term. With no obvious competitors, Sisi appears certain to win.
Nour was founded in the heady days of democratic idealism after Hosni Mubarak was overthrown in 2011, and came second to the Brotherhood in 2011 parliamentary elections.
Its dilemma is how to keep a foothold in the political process, with an eye on the parliamentary election that is likely to follow the presidential poll, without losing credibility among its Islamist voter base.
It has come under fierce attack within the wider Islamist movement for lending its support to the army's decision to depose Mursi after the June 30 protests.
Most recently, it launched a nationwide campaign to promote the new constitution, approved last week in a referendum by more than 98 percent of voters, arguing that the alternative was chaos. Turnout was 38.6 percent.
That constitution stripped out Islamist provisions that the Nour had lobbied for when it helped draft the previous constitution, suspended last July, although Nour said the new constitution safeguarded the role of Islamic law.
"If Sisi runs, yes, they would find it a bit difficult to convince their base to back him," said Amr Hashim Rabie of the Al Ahram Center for Strategic and Political Studies, a state-run think-tank. "They are not one stream. This is their problem."
Borhami denied reports that few Salafists had voted despite the Nour Party's campaign for a "yes" vote, saying their participation could not be measured by the number of bearded men and veiled women lining up outside polling stations.
As an ultra-orthodox Islamist party that espouses a puritanical vision of Islam, the Nour was a sometime ally of the Muslim Brotherhood in the 2-1/2 years before Mursi was toppled, but the alliance was an uneasy one.
The Nour are political novices compared to the Brotherhood, having emerged from the politically quietist Dawa Salafiya. After the 2011 elections, they used their influence in officialdom to press for Islamist changes to the system of government.
Their political success was partly based on the charity network operated by Borhami's Dawa Salafiya and the appeal of its ultra-orthodox vision among deeply conservative sections of society that saw the Brotherhood as too politically pragmatic.
Having backed moderate Islamist Abdel Moneim Abol Fotouh in the first round of the 2012 presidential election, the Nour campaigned for Mursi in the run-off against Mubarak's last prime minister Ahmed Shafik, helping to propel him to victory.
But it refused to take part in pro-Mursi rallies and protests last year, and approved the army-designed political transition plan unveiled after he was deposed.
The party's deputy leader appeared alongside Sisi when he announced on July 3 that Mursi had been removed from power.
The Nour Party has said it has no intention of contesting the presidency, rejecting the model of Islamist rule offered by the Brotherhood.
"The experiment failed. We could have fielded a candidate of our own (in the 2012 election), but we rather saw it was not the appropriate time to do so," Borhami said.
Instead, Nour is setting its sights on the parliamentary election expected later this year.
"We have won respect from the people for our moderate positions," Borhami said. "Maybe we lost some support from within the Islamic movement, but many have admired the party's policies." (Editing by Tom Perry and Kevin Liffey)