* Second stage of referendum to be held on Saturday
* More support for measure likely in second round
* Islamists say constitution vital to move forward
* Opposition say charter ignores minority rights
* Parliamentary election to follow if constitution passed
By Shaimaa Fayed and Tamim Elyan
CAIRO, Dec 17 (Reuters) - President Mohamed Mursi has won initial backing from Egyptians for a new constitution that he hopes will steer the country out of crisis, but which opponents say is an Islamist charter that tramples on minority rights.
A first day of voting in a referendum on the draft basic law resulted in 56.5 percent 'Yes' vote, Mursi's political party said. An opposition official conceded that Egyptians voting on Saturday appeared to have backed the measure.
Next Saturday's second set of balloting is likely to give another "yes" vote as the voting then will be in districts generally seen as even more sympathetic towards Islamists, and that would mean the constitution should be approved.
But the apparent closeness of the early tally gives Mursi only limited comfort as it exposes deep divisions in a country where he needs to build a consensus for tough economic reforms.
If the constitution passes, national elections can take place early next year, something that many hope will usher in the stability that Egypt has lacked since the fall of Hosni Mubarak nearly two years ago.
"The referendum was 56.5 percent for the 'yes' vote," said a senior official in the operations room set up by the Brotherhood's Freedom and Justice Party to monitor voting.
A statement from the opposition National Salvation Front did not explicitly challenge the Brotherhood's vote tally, saying instead that voting malpractices meant a rerun was needed.
Rights groups reported abuses such as polling stations opening late, officials telling people how to vote, and bribery. They also criticised widespread religious campaigning that portrayed "No" voters as heretics.
A joint statement by seven human rights groups urged the referendum's organisers "to avoid these mistakes in the second stage of the referendum and to restage the first phase".
Mursi and his backers say the constitution is vital to move Egypt's democratic transition forward. Opponents say it is too Islamist and ignores the rights of minorities, including the Christians who make up 10 percent of the population.
The build-up to Saturday's vote was marred by violent protests. Demonstrations erupted when Mursi awarded himself extra powers on Nov. 22 and then fast-tracked the constitution through an assembly dominated by his Islamist allies and boycotted by many liberals.
However, the vote passed off calmly, with long queues in Cairo and other places, though unofficial tallies indicated turnout was around a third of the 26 million people eligible to vote this time. The vote is being held over two days because many of the judges needed to oversee polling staged a boycott in protest.
The opposition had said the vote should not have been held given the violent protests. Foreign governments are watching closely to see how the Islamists, long viewed warily in the West, handle themselves in power.
"BLOOD AND KILLINGS"
"It's wrong to have a vote or referendum with the country in the state it is in - blood and killings, and no security," said Emad Sobhy, a voter who lives in Cairo.
As polls closed late on Saturday, Islamists attacked the offices of the newspaper of the liberal Wafd party, part of the opposition National Salvation Front coalition that pushed for a "no" vote.
Violence in Cairo and other cities plagued the run-up to the referendum. At least eight people were killed when rival factions clashed during demonstrations outside the presidential palace earlier this month.
"The nation is increasingly divided and the pillars of state are swaying," opposition politician Mohamed ElBaradei wrote on Twitter. "Poverty and illiteracy are fertile grounds for trading with religion. The level of awareness is rising fast."
A narrow loss could still hearten the leftists, socialists, Christians and more liberal-minded Muslims who make up the disparate opposition, which has been beaten in two elections since Mubarak was overthrown last year.
They were drawn together to oppose what they saw as a power grab by Mursi as he pushed through the constitution. The National Salvation Front includes prominent figures such as ElBaradei, former Arab League chief Amr Moussa and firebrand leftist Hamdeen Sabahy.
In order to pass, the constitution must be approved by more than 50 percent of those casting ballots. There are 51 million eligible voters in the nation of 83 million.
The army deployed about 120,000 troops to protect polling stations. While the military backed Mubarak and his predecessors, it has not intervened in the present crisis.