* Six dead as bitter confrontation grips central Cairo
* Western powers crank up calls on Mubarak to start handover
* Trial of strength as govt appeals for return to normality
* U.S.-backed army remains cautious, weighing its options
(Adds detail, edits)
By Jonathan Wright and Marwa Awad
CAIRO, Feb 3 (Reuters) - A bitter and, by turns, bloody confrontation gripped central Cairo on Thursday as armed government loyalists fought pro-democracy protesters demanding the overthrow of President Hosni Mubarak.
At least six people were dead and 800 wounded after gunmen and stick-wielding Mubarak supporters attacked demonstrators camped out for a tenth day on Tahrir Square to demand the 82-year-old leader immediately end his 30-year rule.
A literal stone's throw from the Egyptian Museum, home to 7,000 years of civilisation in the most populous Arab state, angry men skirmished back and forth with rocks, clubs and makeshift shields, as the U.S.-built tanks of Mubarak's Western-funded army made sporadic efforts to separate them.
Away from the lenses of global media focused on Tahrir Square, a political battle was being fought with implications for competing Western and Islamist influence over the Middle East and its oil. European leaders joined the United States in urging their long-time Arab ally to start handing over power.
His government, newly appointed in a reshuffle that failed to appease protesters, stood by the president's insistence on Tuesday that he will go, but only when his fifth term ends in September. Mubarak continues to portray himself as a bulwark against anarchy, or a seizure of power by Islamist radicals.
The opposition won increasingly vocal support from Mubarak's long-time Western backers for a swifter handover of power.
"This process of transition must start now," the leaders of Britain, France, Germany, Italy and Spain said in a statement.
U.N. Secretary General Ban Ki-moon added his voice.
They all echoed the message U.S. President Barack Obama said he gave Mubarak in a phone call on Tuesday. U.S. officials also condemned what they called a "concerted campaign to intimidate" journalists, after many were attacked by government loyalists.
Opposition leaders including the liberal figurehead Mohamed ElBaradei and the mass Islamist movement the Muslim Brotherhood said again that Mubarak must go before they would negotiate.
TRIAL OF STRENGTH
As he tended to some of those on the square, doctor Mohamed al-Samadi voiced anger: "They let armed thugs come and attack us. We refuse to go. We can't let Mubarak stay eight months."
Protesters, who numbered some 10,000 on Tahrir Square on Thursday afternoon, have called major demonstrations for Friday. Many formed human chains across roads to seal off the square.
This is a trial of strength in which the army has a crucial role as its commanders seek to preserve their institution's influence and wealth in the face of massive popular rejection of the old order, widely regarded as brutal, corrupt and wasteful.
The government, which rejected assumptions by foreign powers that it had orchestrated the attacks on demonstrators, seemed to be counting on winning over the sympathy of Egyptians feeling the pinch of unprecedented economic dislocation.
"I just want to see security back on the streets so that I can go on with my life," said Amira Hassan, 55, a Cairo teacher. "It makes no difference to me whether Mubarak stays or leaves."
New Prime Minister Ahmed Shafiq sought to appease anger at home and abroad by apologising for the violence and promising to prevent a repeat. But he insisted he did not know the culprits.
Vice President Omar Suleiman, seen as a possible interim successor to Mubarak, took up the theme, promising to release detained demonstrators and to punish those who fomented trouble.
He also confirmed that Mubarak's businessman son Gamal would not run for president to succeed his father. Ten days ago, that would been shock news. It surprised no one after the uprising.
The protesters in Tahrir Square, dominated now by a youthful hard core including secular middle-class graduates and mostly poorer Islamist activists from the Brotherhood, barely listened. They have been inspired by the example of Tunisia, where veteran strongman Zine al-Abidine Ben Ali was forced to flee last month.
But many other Egyptians have more respect for Mubarak and seem willing to let him depart more gracefully in due course.
Those supporting the calls for constitutional change and free elections saw the violence, unleashed on Wednesday by men they assume to be secret policemen and ruling party loyalists, as the desperation of a president who cannot count on his army.
It was a "stupid, desperate move", said Hassan Nafaa, a political scientist and leading opposition figure. "This will not put an end to the protests," he said. "This is not the Tahrir Square revolution, it is a general uprising."
Though less numerous than earlier in the week, there were also demonstrations in Suez and Ismailiya, industrial cities where inflation and unemployment have fuelled the sort of dissent that hit Tunisia and which some believe could ripple in a domino effect across other autocratic Arab states.
ARMY ROLE
Many analysts see the army seeking to preserve its own position by engineering a smooth removal of Mubarak, a former air force commander. Its course is unclear. On Monday it gave protesters heart by pledging to let them demonstrate.
But on Wednesday, troops stood by as Mubarak supporters charged Tahrir Square on horseback and camels, lashing out at civilians. After dark, several demonstrators were shot dead.
Only on Thursday morning did soldiers set up a clear buffer zone around the square to separate the factions. But that did not prevent new clashes, as groups pelted each other with rocks.
Many believe Mubarak's efforts to hang on may create strains within the army, which may seek to cut short the confrontation.
"There is a real threat to the integrity of the armed forces, the longer this goes on," said Faysal Itani of Exclusive Analysis. "The pressure on the army must be intense to put him on a plane or in a villa ... I'd give him seven to 10 days."
Support for a new order is far from unanimous, however.
Many of the 80 million Egyptians have much to lose from change, whether businesspeople enjoying lucrative concessions in the mixed economy or those employed by the extensive apparatus of the state and its security forces. An even greater number is losing patience with unrest after 10 days of disrupted business.
"My work depends on tourists and there aren't any tourists coming any more," said Ragab Abdel Hamid Mansour, a 48-year-old cruise boat owner on the Nile in Cairo. "I want those protests to end now, and even not tomorrow. I can't live."
Egypt was the first and so far almost the only Arab state to make peace with Israel. Prime Minister Benjamin Netanyahu says revolution in Cairo could create an Iranian-style theocracy.
Egyptian Health Minister Ahmed Samih Farid said six people died and 836 were wounded in the Cairo fighting. An estimated 150 people have been killed since last Tuesday.
Oil prices have climbed on fears the unrest could spread to affect oil giant Saudi Arabia or interfere with oil supplies from the Red Sea to the Mediterranean through the Suez Canal.
Brent crude passed $103 a barrel on Thursday.
On Thursday, tens of thousands of pro-and anti-government protesters squared off in the Yemeni capital Sanaa. (Reporting by Edmund Blair, Samia Nakhoul, Patrick Werr, Dina Zayed, Marwa Awad, Shaimaa Fayed, Alexander Dziadosz, Yasmine Saleh, Sherine El Madany, Yannis Behrakis, Jonathan Wright, Andrew Hammond, Tom Perry and Alison Williams in Cairo, Myra MacDonald in London and Leigh Thomas in Paris; writing by Alastair Macdonald; Editing by Jon Boyle)