By Maggie Fick

CAIRO (Reuters) - Egypt's Islamist-dominated parliament must move quickly to adopt judicial reforms that have sparked a revolt by judges, the deputy leader of the Muslim Brotherhood's political arm argued on Friday.

The proposed reforms, which would get rid of more than 3,000 judges by lowering the retirement age, have widened the rift between President Mohamed Mursi's government and a judiciary seen by its critics as a last bastion of the old regime that was toppled in the 2011 revolution.

Essam el-Erian, a member of parliament from the Freedom and Justice Party which dominates the chamber, said in a Facebook post that passage of a new law defining the powers of the judiciary should not be delayed.

Judges have slammed the Islamist-led parliament for attempting to pass the changes, put forward by the moderate Islamist Wasat Party. But Erian said the upper house had the legislative authority to do so, in consultation with the judiciary.

The lower chamber of parliament was dissolved last year by a court ruling, thrusting the upper house into the position of passing legislation, although the opposition has questioned its right to do this.

New elections were postponed by a court ruling, and Mursi has said they could be held in October.

A senior official of Egypt's biggest hardline Islamist party on Friday rejected the reforms under consideration. Abdullah Badran of the Nour Party wrote on Facebook that the constitution required greater consultation with the judiciary in changing the law.

Separately, a judge who served as the head of the embattled constitution-drafting body said reforms should be postponed until after a new parliament is elected, state news agency MENA reported.

Outside the High Court, which was the scene of clashes last week between Islamist protesters and their opponents, a small crowd of demonstrators gathered on Friday to chant for the judiciary's independence. Islamist parties postponed their latest round of protests calling for it to be purged.

(Additional reporting by Ahmed Tolba; Editing by Mark Trevelyan)