CAIRO, Dec 7 (Reuters) - Egypt's main opposition coalition said on Friday it would not take part in a dialogue proposed by President Mohamed Mursi to end a crisis sparked by the Islamist leader's decision to expand his powers, a senior member of the group said.

Speaking in a televised address on Thursday night, Mursi had invited political leaders and others for talks on Saturday and said plans for a Dec. 15 referendum on a new constitution were on track despite clashes that killed seven people.

"The National Salvation Front is not taking part in the dialogue, that is the official stance," Ahmed Said, one of the leading members of the coalition who also heads the liberal Free Egyptians Party, told Reuters.

Prominent reformist Mohamed ElBaradei and the Wafd party, both members of the liberal-minded coalition, said they would not be taking part.

"I appeal to all national forces not to participate in dialogue that lacks the basics of real dialogue, we are for dialogue that is not based on arm-twisting and imposing a fait accompli," ElBaradei said in a message on Twitter.

Mursi's administration insists the president's actions were aimed at speeding up the transition to democracy that had been hampered by a judiciary still packed with appointees of ousted President Hosni Mubarak.