* Head of Brotherhood party says crisis ending soon
* Party seeking alliances with liberals in parliament vote
* Constitution can be amended, not "eternal"
* Sees "common ground", despite anti-Mursi protests
By Tom Perry
CAIRO, Dec 4 (Reuters) - The Muslim Brotherhood's political party believes the crisis buffeting Egypt is nearly over and is turning its attention to building alliances with liberal foes on the other side of the struggle for the country's future.
Saad al-Katatni, head of the Brotherhood's Freedom and Justice Party (FJP), said approval of a new constitution in a Dec. 15 referendum would end the turmoil set off by President Mohamed Mursi's assumption of new powers in a Nov. 22 decree.
"The crisis we have suffered for two weeks is on its way to an end, and very soon, God willing," Katatni said on Tuesday.
Mursi's decree has exposed a deep split between Islamists and liberals and others who oppose them. But the Brotherhood and its Islamist allies have proved their electoral muscle in previous votes since Hosni Mubarak's overthrow 22 months ago and even their opponents expect them to win the referendum.
In an interview at the FJP headquarters, Katatni outlined his party's plan for what comes next: an effort to build alliances with secular-minded groups for parliamentary elections to take place once the new constitution is approved.
His remarks signal an impending Brotherhood effort to build bridges with people who have taken to the streets against Mursi's decree, accusing the president and his Islamist backers of seeking to set up a new dictatorship.
With mistrust of the Brotherhood running deep, the initiative could face an uphill struggle. Yet Katatni said finding common ground was vital to Egypt's future.
"Our preferred option is that the alliance not be ideological so that we don't have a split in the nation: a group representing the Islamists and a group representing (the others)," Katatni said. "This represents a danger."
He said he would hold talks with what he described as "influential people in society" to heal discord. "The interim period is nearly over and we will start a new period that needs consensus. I think this is my duty."
Katatni added: "We are trying to find common ground between the liberal and Islamist forces on a political programme."
In the latest crisis, the Brotherhood has fallen back on the support of more hardline Salafi Islamist parties. These have cooperated in driving through the new constitution written by an assembly dominated by Islamists. The Salafi parties also joined a rally by Mursi supporters in the street on Saturday.
Katatni's remarks suggested that the FJP's cooperation with Salafis would not last into the election campaign. But the Brotherhood may still find it difficult to convince non-Islamists it can be trusted, despite its pragmatic approach.
Mursi's decree has deepened the division between secular-minded parties and the Islamists. Up to 10,000 demonstrators gathered outside Mursi's palace on Tuesday, the latest in a series of protests ignited by the Nov. 22 decree.
Having won the presidency by a slim margin, Mursi stands accused by liberal, leftist and socialist parties of breaking his campaign promise to be a president for all. The anger has been compounded by the Brotherhood effort to fast-track a constitution the non-Islamists says has ignored their concerns.
CONSTITUTION "NOT ETERNAL"
Katatni was confident the new constitution would be approved in the Dec. 15 referendum called by Mursi on Saturday. "The people want stability. They want a constitution," he said.
But he added that the draft could always be changed were a fifth of parliament to propose an amendment. The proposal must then be approved by a two-thirds majority, he said. "Constitutions are not written to be eternal," he declared.
Any amendments must also be approved in a referendum.
Katatni foresaw protests lasting until the referendum.
"People will express themselves - their satisfaction or anger - until the referendum comes, and after the referendum, I think matters will stabilise for some time," he said.
"When parliamentary election nominations begin, the competition will re-emerge. Then the parliament will be formed.
"At that point, matters will stabilise and I hope they will stay stable so the economy can recover, investment can flow and tourists return," he said.
Wary of the Salafi Islamist parties, the Brotherhood entered electoral alliances with secular-minded groups including leftist parties in legislative polls held a year ago. That parliament was dissolved in June because of what a court ruled was a flaw in the election law.
Under the draft constitution, the new parliament will play a major role in shaping the next government, heightening the need for agreement on a shared programme in advance, said Katatni.
"We have tasked committees to produce a programme and we are trying to market it to other partners to go into the elections together," he said. "I am optimistic about what is happening in Egypt now," he said. "There are many areas of commonality." (Editing by Alistair Lyon)