By Edmund Blair and Yasmine Saleh
CAIRO, Dec 12 (Reuters) - With a bust of Egypt's former President Gamal Abdel Nasser in his office, opposition politician Hamdeen Sabahy has a knack for the kind of rousing rhetoric his nationalist hero employed to inspire the public.
The one-time student leader who founded the Popular Current, a movement that has started to gain influence across the country of 83 million, may be one of the biggest winners from a crisis that has engulfed Islamist President Mohamed Mursi after he expanded his powers and sparked nationwide protests.
Whether Sabahy or any other opposition figure can emerge as a credible leader of those who reject Mursi and his fellow Islamists may determine Egypt's future course.
"We will never differentiate in this nation between Muslim and Christian, men and women, those in the countryside or in the cities," Sabahy told a crowd this month in Tahrir Square where protesters accuse Mursi of driving a wedge between Egyptians of different faiths and opinions.
"In one hand" and "The people want to bring down the regime" they chanted back at the leftist politician on the podium.
Egypt's disparate opposition, trounced in two elections by well-organised Islamists since Hosni Mubarak was overthrown almost two years ago, have been united by the latest crisis and have proved that Mursi's Muslim Brotherhood and his allies do not have a monopoly on mobilising Egyptians.
That is heartening to Christians, moderate Muslims and more liberal-minded Egyptians angry at Mursi for pushing through a constitution drafted by an assembly dominated by his Islamist allies. It will go to a referendum on Saturday.
Sabahy, 58, sits alongside several other well-known personalities in the opposition coalition, the National Salvation Front, that was thrown together by the political upheaval. Together they have brought tens of thousands onto the streets, even if not quite as regularly as the Islamists have done.
Like Sabahy, Nobel Peace Prize laureate Mohamed ElBaradei, 70, and Amr Moussa, 76, a former foreign minister under Mubarak and then Arab League chief, have grown in standing.
But neither engenders the enthusiasm on the street that greets Sabahy, who has said he rose from the son of a peasant to his position now because of the policies of Nasser, who enthralled Egyptians and Arabs in the 1950s and 1960s.
In another demonstration in Tahrir Square, the cauldron of the anti-Mubarak uprising, ElBaradei addressed protesters this month. But instead of the fluid and gesticulating performance of Sabahy, the former head of the U.N. nuclear agency read his message from notes, drawing muted cheers.
Moussa has won credit for actively engaging in the constitution drafting process until withdrawing with others from the assembly, but he still struggles to shake off his links to Mubarak's discredited government.
"I ask for calm. Today we are in a situation that cannot bear division," ElBaradei told a news conference by the Front when Moussa, standing next to him, was accused by a heckler of being a member of the "feloul", the derisive Arabic term referring to remnants of Mubarak's order.
Yet there is still no clear figurehead that can claim the mantle of leader of the opposition. Nor can any group whether Sabahy's Popular Current movement or ElBaradei's Dostour (Constitution) Party claim to speak for all opposition ranks.
The unity of these politicians for now is based on agreement on what they oppose with little sign yet that the united front will stretch much beyond that and to a common platform in elections ahead.
"The lack of leadership is still a problem facing them," said Hassan Nafaa, a liberal-minded professor at Cairo University, adding the Front "is mainly united by this crisis".
"Everybody understands there is a real danger facing all of them, there is a risk that this constitution might lead to total control of Muslim Brothers and their allies," he said.
On the street, opponents of Islamists praise the role of the Front but fear opposition ranks will fragment as elections loom, splitting their vote which damaged them in the parliamentary and presidency races.
"The Front is standing with us in this crisis," said Ahmed Mohamed, a 24-year-old banker protesting at the presidential palace, whose walls were daubed with anti-Mursi graffiti.
"But when election time comes, I doubt they will run together as they are so different and so far failed to come up with a structure that shows who is the leader," he said.
The opposition has struggled to organise in the post-Mubarak turmoil, and often been accused of relying too heavily on well-known personalities rather than getting down to the more gritty business of building a grass-roots network to get out the vote.
"The silent majority is mobilized now, but we don't know whether those who rushed to the presidential palace will recognise the united Front as their leader or are just mobilised by hatred of the Muslim Brotherhood," said Professor Nafaa.
Opponents have struggled to reach many ordinary Egyptians when faced with the social and charity network built up by the Brotherhood over eight decades, even when the group was repressed and hounded under Mubarak and his predecessors.
ElBaradei, a bespectacled and eloquent diplomat, who returned to Egypt in 2010 from his home in Vienna where he ran the International Atomic Energy Agency, had raised hopes in the opposition that he would lead those against Mubarak's rule.
But critics say he never quite lived up to that billing, although his party members have been prominent among protesters in the crisis now, suggesting he is building a following.
ElBaradei pulled out of this year's presidential race saying there was no point running when a constitution was not in place to define the president's job. Detractors said it was because he lacked a support base as he spent too much time abroad.
Sabahy and Moussa did run. But Moussa, widely praised when head of the Arab League for his tirades against Israel and seen as a front-runner early in the race, found his vote cratered on election day. That was largely blamed on his struggle to convince Egyptians he marked a real break with the past.
Sabahy, however, was one of the biggest surprises, coming from behind to reach third place and narrowly missing a run-off. Some analysts say that good showing was partly because he was the only prominent candidate who was not from the Islamist camp and had no links to Mubarak's rule.
He said the Front could presage a more united approach in the parliamentary vote. "There is an agreement over a national Egyptian project that no one should dominate or be excluded from," he said at his movement's headquarters.
Showing a popular touch, he criticised the draft constitution he said was polarising the nation but also laid into Mursi's tax rises, that the president implemented and then withdrew within hours because of a public backlash.
"What Mursi did was a big shock to a large sector of the public," he said.
Yet, while the Front may have raised the profile of opposition leaders questions remain about how rivals of Mursi and his Islamist allies will maintain cooperation seen as vital if they are really to challenge Islamists in future votes.
"The National Salvation Front can't be anything more than it already is," said Shadi Hamid of the Brookings Doha Centre. "It is not going to be an institutionalised movement because the three leading figures don't agree on that much."
Hamid said liberal politicians needed to move beyond the personality politics. Although Sabahy's Popular Current was building a broader base, Hamid said the leftist had yet to show he could fight an election "that goes beyond fiery speeches and the figure of Hamdeen Sabahy."