* Need to pass election law before vote date set
* Differences over timing, schedule of ballot
* Transition peaceful in contrast with Egypt, Libya
By Tarek Amara
TUNIS, April 8 (Reuters) - Tunisian Islamist and secular parties have begun a parliamentary debate on an election law, the final step before setting a ballot date to complete a transition to democracy in the country that lit the fuse of Arab popular uprisings.
The elections, expected later this year, will be only the second ballot since the 2011 revolt that ousted autocrat Zine el-Abidine Ben Ali, and the first since the adoption of a new constitution praised internationally as a democratic model.
Debate started on late on Monday, with hundreds of proposals already presented for inclusion, and is expected to last as long as two weeks before an election date can be set.
"There are a lot of differences, and we have received around 500 proposals for inclusion to adjust the law that we will be debating now," said Kalthoum Badredine, an assembly member from the Islamist Ennahda party.
Most of the differences are related to positioning by rival Islamists and the secular Nida Tounes party over whether to hold separate presidential and parliamentary elections. Smaller parties want ex-Ben Ali regime officials excluded from the vote.
Three years after its revolt, Tunisia is in its final stages of democratic evolution, with a caretaker government in power after a compromise between Islamists and secular opponents to end a political crisis and prepare for elections.
That agreement between contrasts sharply with Libya and Egypt, which have struggled with street turmoil and political instability since ousting their own long-standing rulers.
Chafik Sarsar, head of the Independent Election Commission (ISIE), said last month that presidential and parliamentary elections would go ahead as planned later this year despite delays in approving a new election law.
The ISIE, the independent body for overseeing elections, was formed in January. Officials said the authorities were seeking to register more than 4.2 million voters.
After months of crisis sparked by the killing of two secular opposition leaders, Ennahda resigned in January under an agreement with Nida Tounes to make way for a caretaker government which will stay in power until the vote.
Ennahda, led by a respected Islamist scholar who spent years in exile in Britain, and Nida Tounes, headed by a former Ben Ali official, are the two main political forces expected to lead in the elections. (Writing by Patrick Markey; Editing by Mark Heinrich)