(Reuters) - Egypt´s constituent assembly held its first meeting on Monday in the debating chamber of the dissolved parliament in a show of defiance against the army´s assumption of legislative powers.

The assembly is due to write a new constitution as part of a transition to democracy engineered by the generals who took power after the overthrow of President Hosni Mubarak´s autocratic government last year.

But that transition was thrown into disarray last week when a court of Mubarak-era judges ruled that the parliamentary election was invalid and the chamber must be dissolved.

On Sunday, the ruling military council issued a decree allowing it to write laws and to name a new constituent assembly if necessary, prompting some analysts to say the generals were insuring themselves against a possible Islamist win when presidential election results are announced on Thursday.

Islamists and liberals united to denounce a "military coup" and parliamentary speaker Saad al-Katatni said parliament could only be rendered void by popular referendum.

"We are holding on to this constituent assembly. It is the only gain we took away from the legitimate parliament," said liberal MP Mohamed el-Sawy, one of the 100 people appointed by parliament to write the democratic constitution.

At its inaugural meeting, the assembly named as its chairman Hossam El Gheriany, who is Egypt´s top judge as head of the Supreme Judicial Council, and agreed to meet again on Saturday.

Officially, the constitution writing process is unaffected by the removal of parliament.

But the army´s decree gives it the right to form a new constitution- writing body if the current one "encounters any obstacles in completing its role" and to oppose any article that contradicts the "goals of the revolution".

"The army will try to use the first opportunity to get rid of it and form a new assembly," said Gamal Abdel Gawad, politics professor at the American University in Cairo.

Analysts say the army might be seeking to secure a special status in the next constitution to protect the economic interests and prestige it has maintained since a 1952 revolution against the monarchy.

The constituent assembly comprises members of parliament as well as constitutional experts, judicial figures, Christian and Muslim clerics, union members and representatives of the army, police, government and Egypt´s youth.

The assembly´s make-up is itself controversial; most liberals and leftists have withdrawn from it because they say it is biased towards the Islamists who dominated the dissolved parliament, and fails to represent Egypt´s diverse social groups fairly.

Islamist Mohamed Morsy and former air force commander Ahmed Shafik both claim to have won the presidential election run-off. (Editing by Tom Pfeiffer and Kevin Liffey) (© Thomson Reuters 2012. 06/18/12)