FACTBOX: Scenarios in Israel PM Olmert's legal troubles

(Reuters) - A police investigation covered by a sweeping media gag order has sparked intense speculation that Israeli Prime Minister Ehud Olmert might have to leave office.

Following are some possible scenarios:

* Olmert has weathered other investigations, none of which has led to indictment. Next election not due until 2010, though Olmert faces opposition, including within his own coalition, to steps he might take to make peace with the Palestinians by a target date of end-2008 set by U.S. President George W. Bush.

* If indicted, Olmert would face even stronger calls to resign. He could refuse and could also step aside temporarily for up to 100 days while his deputy, Tzipi Livni, took over.

* Olmert's centrist Kadima party has no mechanism by which to unseat him as leader. If he lost the confidence of his coalition cabinet, however, they could drive a parliamentary no confidence vote that would bring down the government and give President Shimon Peres a chance to appoint a new prime minister.

* If Olmert chose to resign, Peres could name a replacement after consultation with leaders of parliamentary parties. The likely frontrunner is Livni, the foreign minister. Ehud Barak, leader of Kadima's main coalition partner Labour, is not a member of parliament and cannot therefore be prime minister.

* If the present coalition breaks up, Peres could turn to a leader willing to forge a different line-up of alliances among the 12 groups in parliament. Of 120 seats, Kadima has 29, Labour 19 and the right-wing opposition Likud 12. However, if no leader could secure a parliamentary majority an election would follow.

* An election must be held within five months of the Knesset voting to dissolve itself. In practice, that gap is shorter. Polls show Likud would emerge strongest if a vote were held now.

(Writing by Avida Landau, Editing by Dominic Evans)