* Mursi to address nation
* Says most Egyptians back decree at centre of crisis
* Brotherhood sees quick constitution as way out of crisis
* Critics see move to wrap it up as an escalation
* Tahrir Square sit-in enters day seven
By Tom Perry and Marwa Awad
CAIRO, Nov 29 An assembly charged with writing Egypt's new constitution began voting on its final draft on Thursday, a process President Mohamed Mursi hopes will help to end a crisis which erupted when the Islamist gave himself sweeping new powers.
Mursi's decree last week halting court challenges to his decisions, which provoked protests and violence across the country, will lapse if Egyptians approve the new constitution.
Speedy completion of the draft would allow a referendum to be held as soon as mid-December. But Mursi's opponents have attacked it as an attempt to rush through a text they say has been hijacked by the Muslim Brotherhood and its allies.
In an interview with Time, Mursi said the majority supported his decree but added: "If we had a constitution, then all of what I have said or done last week will stop."
The president is expected to speak to the nation later on Thursday in an effort to ease the crisis, which has set off a week of protests and threatens to derail some early signs of an economic recovery after two years of turmoil.
Two people have been killed and hundreds injured in the protests since last Thursday's decree, which deepened the divide between the newly-empowered Islamists and their opponents.
Setting the stage more tension, the Muslim Brotherhood and its Islamist allies have called for pro-Mursi rallies on Saturday. But officials from the Brotherhood's party changed the venue and said they would avoid Tahrir Square, where a sit-in by the president's opponents entered a seventh day on Thursday.
The Brotherhood, that backed Mursi for president in June elections, hopes to end the crisis by replacing the controversial decree with an entirely new constitution.
"MAY GOD BLESS US"
"May God bless us on this day," Hossam el-Gheriyani, the speaker of the constituent assembly, told members at the start of the session to vote on each of the 234 articles in the draft, which will go to Mursi for approval and then to the plebiscite.
It is a gamble based on the Islamists' belief that they can mobilise voters to win the referendum. They have won all elections held since Hosni Mubarak was toppled last year.
But critics say the bid to finish the constitution quickly could make matters worse.
The constitution is one of the main reasons the Islamists are at loggerheads with opponents who are boycotting the 100-member constitutional assembly, saying their voices were not being heard.
The assembly's legitimacy has been called into question by a series of court cases demanding its dissolution. Its standing has also suffered from the withdrawal of members including church representatives of the Christian minority and liberals.
The Brotherhood argues that approval of the constitution in a referendum would bury all arguments about both the legality of the assembly and the text it has written in the last six months.
Once the assembly backs the draft it will go to Mursi for approval, a step expected at the weekend. He must then call the referendum within 15 days. If Egyptians approve the constitution, legislative powers will pass straight from Mursi to the upper house of parliament, in line with an article in the new constitution, assembly members said.
The draft injects new Islamic references into Egypt's system of government but keeps in place an article defining "the principles of sharia" as the main source of legislation - the same phrase found in the previous constitution.
Among other historic changes to Egypt's system of government, it caps the amount of time a president can serve at two terms, or eight years. Mubarak ruled for three decades. It also introduces a measure of civilian oversight - not nearly enough for the critics - over the military establishment.
Activists highlighted other flaws such as worrying articles pertaining to the rights of women and freedom of speech.
"There are some good pro-freedoms articles, but there are also catastrophic articles like one that prevents insults. This could be used against journalists criticising the president or state officials," said human rights activist Gamal Eid.
"We wanted Egyptians to get more freedoms and less presidential powers and were unhappy with the end result in those areas," said Edward Ghaleb, who had been sitting on the assembly as a representative of the Coptic Orthodox church.
New parliamentary elections cannot happen until the constitution is passed. Egypt has been without an elected legislature since the Islamist-dominated lower house was dissolved in June.
"The secular forces and the church and the judges are not happy with the constitution; the journalists are not happy, so I think this will increase tensions in the country," said Mustapha Kamal Al-Sayyid, a professor of political science at Cairo University. "I don't know how the referendum can be organised if the judges are upset," he added.
Egyptian elections are overseen by the judiciary.
The decree issued by Mursi worsened already tetchy relations with judges, many of whom saw it as a threat to their independence. Two courts declared a strike on Wednesday.
Mursi was unrepentant in the interview published overnight, saying 80 0r 90 percent of Egyptians backed him.
"It's not against the people, It's with the people," he said.