BRUSSELS (Reuters) - The European Parliament will elect a new speaker next week in an unusually heated vote that could end a decade-long cooperation between mainstream parties, complicate lawmaking and trigger a reshuffle of top EU jobs.

All eight political groups of the legislature have fielded candidates, but the winner is expected to be one of the two Italians put up by the main center-right and center-left groupings.

Conservative Antonio Tajani, 63, a close ally of Italy's former prime minister Silvio Berlusconi, is the favorite as he can count on the support of the European People's Party, the largest grouping in parliament.

However, unlike past appointments which were agreed in advance by the main parties, he faces a real challenger in Gianni Pittella, 58, who is bidding to succeed predecessor Martin Schulz, also of the center-left.

Breaking from a decade-long convention whereby the major groupings take turns to hold the high-profile job, Pittella has vowed to stimulate genuine debate and to dispel the idea that all main parties in the Parliament are part of a reform-shy establishment.

Pittella also argues that a deal to make Schulz, a German Social Democrat, head of the parliament in 2014 implied that the Socialists were entitled to hold at least one top EU job.