* Secular opposition keeps stakes high over crisis talks
* Union mediator due to meet Islamist leader again
* Opposition parties plan mass protest for Saturday
By Tarek Amara
TUNIS, Aug 23 (Reuters) - Tunisia's secular opposition said on Friday that the governing Islamists must quit power before they would join negotiations to resolve the country's worst crisis since its Arab Spring revolt, declaring otherwise the talks would be a waste of time.
Opposition leaders said an agreement in principle by the Islamist party Ennahda on Thursday to start talks soon with the mediation of the country's powerful UGTT trade union federation was only a government attempt to buy time.
Commentators said Ennahda's apparent concessions this week kindled hope that Tunisia, the birthplace two-and-a-half years ago of the Arab Spring revolts, might find a consensus to save its nascent democracy rather than see it collapse as in Egypt.
However, as rival parties squabbled over the UGTT offer to mediate, opposition groups went ahead with plans for a large rally on Saturday outside the country's constituent assembly in Tunis to pressure the Islamist-led government to quit.
"Any negotiation without the immediate dissolution of the government would be a waste of time," Taieb Baccouche, secretary general of the main opposition party Nida Tounes, said after meeting UGTT chief Hussein Abassi.
Samir Bettaib, a leader in the "Salvation Front" grouping of several opposition groups, said: "Ennahda continues to manoeuvre ... the only initiative we accept is the announcement to dissolve the government immediately."
Abassi, whose million-strong Tunisian General Labour Union gives him a central role in pressuring the two sides towards consensus, was due to hold another meeting with Ennahda chairman Rached Ghannouchi later on Friday.
RAY OF HOPE?
The current crisis began late last month after the second assassination of a leftist leader this year by suspected Islamist radicals outraged secular groups already opposed to what they called Ennahda's religious agenda, mismanagement of the economy and failure to assure law and order.
Emboldened by the protests that led to the army ouster of Egypt's Muslim Brotherhood President Mohamed Mursi, Tunisian opposition groups stepped up demands for Ennahda to quit.
Ghannouchi announced on Thursday his agreement in principle to meet opposition leaders to discuss the UGTT's proposal that the Ennahda-led government resigns and a technocrat cabinet steps in to organise parliamentary elections.
However, opposition parties insist Ennahda quit before any talks, saying they do not trust it to hold the free and fair poll due at the end of the stalled work on a new constitution, which may be quickly finished if the parties can agree to resolve the crisis.
Ghannouchi, the key player on the Islamist side although he has no official role in the government, has been offering concessions that could pave the way to a caretaker cabinet without appearing to be a defeat for his party Ennahda.
But commentators say it is not clear this will lead to a solution, especially if other factors such as rising popular discontent get out of hand or the two sides cannot agree.
"It's too early for a final verdict, but the evolution of the situation gives a ray of hope for a calming down and a quick end to the standoff," the daily Le Temps wrote.
Although Egypt and Tunisia are both in turmoil over the role of Islamists in their post-revolutionary governments, analysts in Tunisia rule out a Cairo-style military takeover in the small country in North Africa of 11 million people.
Unlike its Egyptian counterpart, the Tunisian army has no tradition of interfering in politics. (Editing by Tom Heneghan and Pravin Char)