* Greek leftist leader vows to cancel Greek bailout
* Tsipras running neck and neck in Sunday vote
* Questions over his leadership skills remain
Alexis Tsipras, the radical Greek leftist who wants to cancel a bailout deal keeping the country afloat if he wins elections on Sunday, is no working class hero.
Born into a comfortable middle class family, Tsipras has a post-graduate degree in engineering but worked only briefly in construction before turning to full-time politics and being handed the SYRIZA party leadership on a platter four years ago.
Since then he has transformed an obscure fringe party into one of the two strongest forces in Greek politics, catapulted into second place in inconclusive elections last month by public rage at tough conditions tied to the 130 billion euro bailout.
For critics, his political career forged in student protests in the 1990s does not give Tsipras the background to govern a country. In 2001, he tried to take part in anti-G8demonstrations in Genoa, one of the emblematic moments of the anti-globalisation movement, but was stopped by Italian police.
His defenders say experienced politicians have run Greece into the ground and new blood is needed.
"So what if he doesn't have the experience?" said SYRIZA deputy Panagiotis Kouroublis. "If he can run a party, he can run a country. Greece has suffered from people who promised one thing and did another."
Tsipras has vowed to scrap the bailout deal but keep Greece in the euro, a task European leaders say is impossible. He has promised to nationalise banks, stop privatisations and freeze any austerity measures demanded by international lenders.
This has struck a chord with Greeks brought to their knees by five years of an austerity-driven recession and despairing at decades of scandals involving mainstream politicians who still enjoy impunity.
SYRIZA is now running neck and neck with the pro-bailout conservative New Democracy party of Antonis Samaras, 61, in a race that may decide whether Greece stays in the euro.
Greece's youngest party leader at 37, Tsipras has had a relatively easy ride to head a leftist movement whose older members suffered persecution or exile from the 1967-1974 period of military rule back to the Nazi occupation of World War II.
By contrast Tsipras has known only life under a democracy. He was born a few days after the military junta fell into an Athens family which owned a small construction business.
Tsipras refused to join a coalition government with other parties after the inconclusive May 6 election, prompting Sunday's repeat vote which opinion polls show he may win.
SYRIZA's performance last month surprised Tsipras as much as the rest of the world, which watched in amazement as Greece's debt crisis turned into a political stalemate threatening the euro currency and shaking world markets.
Party members who rushed to congratulate Tsipras for his success said he had reacted with disbelief: "Are you serious? This is for real?" he was quoted as asking when he discovered SYRIZA had won 16.8 percent in a highly fragmented field.
Analysts said he handled well the transformation of his party from a group that tacitly tolerated anarchists and other far-leftists to one backed by large swathes of the population. Polls showed SYRIZA's support rose about 10 percentage points since the last election.
"Most of his supporters voted for SYRIZA for the first time. The social make-up of the party changed and he managed that well," said Costas Panagopoulos, head of ALCO pollsters.
But Tsipras has done less well in managing his personal success. "He appeared a little arrogant, like the victory was a given," Panagopoulos said. "He has no experience in managing a country and nobody knows how he will do."
Tsipras moderated his rhetoric after the May election, saying he wanted to re-negotiate with lenders rather than scrap the bailout, but soon returned to his more radical speeches.
"As of Monday, the evil forces of internal graft and the foreign loan sharks will stop drafting bailout plans," he said on Tuesday.
Analysts said the hardening of positions may signal he is not ready to govern and would rather wait for the election after Sunday's vote, which he may win outright. A New Democracy-led coalition may not last long with a strong SYRIZA in opposition.
Friends say he is more nervous than he looks. "He used to love slow mornings," said one aide. "Now he jumps up before his alarm clock goes off."
A former Communist party youth member, he joined the SYRIZA coalition of 12 radical leftist groups, including environmentalists and human rights activists, and ran for mayor of Athens in 2006. He didn't win but his strong showing lifted him to the top of the party ranks.
A LEADER AT 33
In 2008, his mentor and then SYRIZA leader Alekos Alavanos virtually handed him the helm at the age of 33, raising more than a few eyebrows among the veteran leftists.
When he attended his first official reception at the presidential palace, he brought as his date a young woman from Sierra Leone, to show the plight of immigrants in Greece.
His youthful looks and refusal to wear a tie to the most formal of events make him stand out in a room of older, traditional politicians.
Tsipras has one child and expecting a second with his partner Betty. The two have not married, in defiance of traditional Greek society. He has openly backed gay marriage and gay adoption.
"He often interrupts party meetings to go pick up his kid," Kouroublis said. "He's very human. He really listens to what you have to say and takes it into account."
While his appeal among Greeks is obvious, foreign politicians view him with scepticism. Greece's partners have issued warnings that unless austerity commitments are met, the financial lifeline will be cut off.
"Foreigners are using a carrot and stick approach with him," an aide said on condition of anonymity. "They won't let Greece go bankrupt and will surely hand us the next loan installment."
A quick European trip after the May 6 election showed Tsipras's main weakness is in dealing with foreign partners.
In France, he said newly-elected Socialist President Francois Hollande had better keep his promises on moderating austerity or he would become a "Hollandreou", alluding to the downfall of former Greek socialist premier George Papandreou.
Critics said it was unwise to alienate a potential good friend of Greece in the euro zone.
Another issue Tsipras must deal with at home is his party being flooded with former socialist trade unionists, bent on stopping reforms and protecting special interests.
"Everyone who wants things to stay as they are is now going to Tsipras," said a former government official. "It's becoming the coalition of the drachma."
Political analysts say the people who rushed to SYRIZA will be easily disappointed and may abandon him if he lets them down.
"His mandate will be to renegotiate the bailout deal and keep Greece in the euro. If he wins he will realise the problem. His image will collapse," said analyst John Loulis. "Public opinion is not in love with Tsipras, it's angry with the others."