Sebastian Scheiner, File, Associated Press
FILE - In this Wednesday, Nov. 30, 2011 file photo, head of Israel's parliamentary opposition Tzipi Livni attends a news conference at the Knesset, Israel's parliament, in Jerusalem. Livni on Wednesday, Jan. 18, 2012, reluctantly called a party leadership race for March 27, injecting a new element of uncertainty into Israel's already unsettled political scene.

JERUSALEM — The head of Israel's main opposition party on Wednesday reluctantly called a leadership primary election for March 27, injecting a new element of uncertainty into Israel's already unsettled political scene.

National polls showing dramatically shrinking support for the Kadima Party pressured party leader Tzipi Livni to start a campaign she had long resisted. Livni appeared to be reacting to a fast-moving series of political developments that could result in early national elections.

National elections are set for late 2013. Public opinion polls suggest Prime Minister Benjamin Netanyahu and his hawkish coalition partners would maintain power if the elections were moved up. But crises threatening two of Netanyahu's partners and the entry of a popular former journalist into the mix have reshuffled the deck.

Livni, who has led Kadima since former Prime Minister Ehud Olmert stepped aside in early 2009 to fight corruption charges, has presided over a party divided by infighting and struggling for relevance. The party, like other centrist rivals, champions the establishment of a Palestinian state, but it has ill-defined views on economic and social issues that have come to the fore.

The animosities tearing the party apart surfaced immediately after news of the leadership election broke. Livni's chief rival Shaul Mofaz, a former defense minister and military chief, accused her of damaging the party with her "indecisive, tired and irresolute conduct."

Then-Prime Minister Ariel Sharon formed Kadima in 2005 when the his hard-line Likud refused to back his unilateral pullout from Gaza that year. Sharon was felled by a stroke a few months later. With Olmert, it governed until the 2009 election, where it won the most votes under Livni but failed to build a centrist coalition, handing the premier post to Netanyahu.

Polls predict that Kadima would not do nearly as well in the next election. Without a clear message and facing several centrist rivals, it appears to be struggling for support. In particular, the arrival of newcomer Yair Lapid, a charismatic former TV personality who last week decided to enter politics, is expected to lure away a significant number of Kadima supporters.

Netanyahu abruptly moved up the leadership race in his own party, in a move some analysts have interpreted as signaling his desire to call early elections, possibly before the U.S. presidential election in November.

Some of his allies are having internal problems that could lead either one to pull out and rob Netanyahu of his parliamentary majority.

His ultranationalist foreign minister, Avigdor Lieberman, might find himself out of a job if his lawyers fail in their hearing before the attorney general this week to fend off threatened corruption charges.

The head of another coalition partner, the ultra-Orthodox Shas, might back early national elections to fend off a potential leadership challenge by his popular predecessor, who left politics to serve a prison sentence for bribery.