By Tamim Elyan and Shaimaa Fayed
CAIRO, Dec 27 (Reuters) - An Islamist minister quit Egypt's government on Thursday, the second cabinet resignation this week as President Mohamed Mursi tries to shore up his authority and gather support for unpopular austerity measures.
An economic crisis and a battle over a new constitution have underlined bitter divisions between Mursi and his opponents and delayed a return to stability almost two years since a popular uprising.
Rivals accuse Mursi, who won Egypt's first freely contested leadership election in June, of polarising society by foisting a divisive, Islamist-leaning constitution on the country and using the autocratic ways of his deposed predecessor Hosni Mubarak.
Deadly violence preceded a referendum on the basic law, dealing a blow to a struggling economy. Mursi's political rivals refused to accept the result - the text won about 64 percent in the vote - and they reject his call for national unity talks.
In a move that may preempt a planned reshuffle by Mursi, parliamentary affairs minister Mohamed Mahsoub announced he was quitting because he disagreed with the slow pace of reform.
"I have reached a clear conclusion that a lot of the policies and efforts contradict with my personal beliefs and I don't see them as representative of our people's aspirations," he said in his resignation letter.
Communications Minister Hany Mahmoud quit earlier this week, citing his inability to adapt to the government's "working culture".
Earlier on Thursday, a Christian member of Egypt's upper house of parliament, Nadia Henry, quit a day after the Islamist-dominated chamber took over legislative authority under the new constitution.
The constitution crafted by an Islamist-dominated assembly is meant to be the cornerstone of a democratic and economically stable Egypt after decades of authoritarian rule. The opposition says it does nothing to protect minorities.
Mursi says the constitution and an upcoming vote to re-elect the lower house of parliament will help end squabbling among feuding politicians.
He and his Muslim Brotherhood allies say ordinary people are fed up with street protests that often turn violent and want the government to focus on urgent bread-and-butter issues.
The strife has cast doubt on the government's ability to push through the spending cuts and tax hikes needed to secure a vital $4.8 billion International Monetary Fund loan.
The Egyptian pound tumbled to its weakest in almost eight years against the dollar this week as people rushed to withdraw savings from banks.
The resignations this week come ahead of a promised cabinet reshuffle. Cabinet sources have told Reuters as many as eight cabinet members from second-tier ministries might go next week.
Mursi is also promising incentives aimed at making Egypt - once a darling of emerging market investors - an attractive place to do business again.
The 270-seat upper house, or Shura Council, holds legislative authority until a new parliament is elected in early 2013. Opposition figures say they fear the Council could issue laws curbing freedoms.
Henry represents Anglican Christians in Egypt. Her resignation underscores fears by Egypt's Christians, who make up about a tenth of its 83 million population, about the gains by Islamists since Mubarak was ousted in 2011.
In a resignation letter published by state media, she said liberal and other minority groups were not represented properly in the chamber.
Under pressure to acknowledge Egypt's diversity, Mursi appointed 90 members including Christians, liberals and women to the Council - alongside figures from the Muslim Brotherhood and ultra-conservative Salafis - last week. Two-thirds of the upper house were already elected in a vote this year.
"We stress again that the nation should achieve internal reconciliation and forget its differences," the Muslim Brotherhood's supreme guide, Mohamed Badei, told Egyptians in his weekly message.
"Let's work seriously to end the reciprocal wars of attrition. We urgently need to unify ranks and group together and focus our capabilities and assets for the general benefit." (Writing by Maria Golovnina; Editing by Tom Pfeiffer)