Former Israeli Prime Minister Ehud Olmert is considering a political comeback to challenge incumbent Benjamin Netanyahu in the upcoming elections, aides said Wednesday.

With new parliamentary polls set for early 2013, Olmert is considered the candidate with the best chance of unseating Netanyahu at the ballot box, despite a precarious legal situation that may stand in his way if he gets elected.

Olmert was recently cleared of the most serious of several bribery allegations that forced him out of office in 2009 but is still bogged down in a separate bribery trial that leaves his political future in doubt.

Olmert was deeply unpopular while in office, but he has enjoyed a revival in recent months, with many fearing he was unfairly removed from office for allegations that ultimately did not stand up in court.

Commentators have also lamented the breakdown in Mideast peace efforts under Netanyahu and wondered whether Olmert, who conducted more than a year of intense negotiations with the Palestinians, might have delivered an agreement if he had not been driven from power.

"I can tell you that he is pondering it and the political system is putting a lot of pressure on him," his former Cabinet secretary and confidante Yisrael Maimon told Israel's Army Radio station.

With Netanyahu's hawkish Likud party far ahead in the polls, Israel's centrist and leftist parties are desperate for a candidate who can unite the fragmented and leaderless opposition parties under an umbrella that can mount a serious challenge.

Analysts predict Olmert is the only candidate who could prevent Netanyahu from a sweeping re-election. Since he stepped down, his Kadima Party has seen its public support evaporate under new leader Shaul Mofaz.

If Olmert jumps back into politics, it is unclear if he will rejoin Kadima or a new political constellation. Kadima lawmaker Dalia Itzik said she hopes Olmert retakes Kadima, with Mofaz's acquiescence.

"I want to see him as the prime minister of Israel and since I know Mofaz and what a responsible man he is, I am sure that at this time we all need to put our jealousies, anger and egos aside and do what is best for Israel," she said.

Former Cabinet Minister and close Olmert friend Haim Ramon is leading the effort to create a new centrist bloc. Ramon confirmed he had reached out to the former prime minister about heading it.

"I am talking to Ehud Olmert. He has obviously not made his decisions and we need to wait patiently," he told Army Radio.

Aware of the threat an Olmert candidacy could pose to Netanyahu, a Likud lawmaker has asked Israel central election committee to urgently discuss whether Olmert is eligible to run.

Olmert was forced out of office nearly four years ago under the cloud of scandal, accused of accepting cash-stuffed envelopes from an American political supporter and allegedly double billing supporters for overseas trips. In July, the court cleared him of those serious allegations, convicting him only on the lesser charge of breach of trust for helping allocate government contracts to a friend's associates. He is still engaged in a separate trial for his alleged role in a Jerusalem real estate bribery case.

His legal trouble leaves his political prospects in limbo.

Emanuel Gross, a legal analyst at the University of Haifa, said Olmert was technically clear to run for office and serve as a lawmaker since the court did not sentence him to jail time or rule that he bears moral turpitude for his actions.

But the later ruling could be appealed in court, he said, and so long as he was entangled in an ongoing trial he was barred from serving as a minister or a prime minister.

"He can head a party," Gross said. "But if that party wins it's not certain that he can head the government."

On Tuesday night, Netanyahu ordered the new parliamentary elections, roughly eight months ahead of schedule.

The immediate reason for the snap elections was the coalition's inability to pass a 2013 budget by a Dec. 31 deadline. But Netanyahu has long been rumored to be leaning toward elections, given his high standings in opinion polls, the lack of a clear rival and fears the economy could weaken next year.

Analysts say Olmert's predicament likely weighed heavily in Netanyahu's decision.

"Don't pay attention to the media spins, it's not the budget, it's not Romney and it isn't Iran. What is driving Netanyahu to the polling stations at almost hysterical speed is Ehud Olmert," columnist Ben Caspit wrote in Wednesday's Maariv daily.

"He knows that the only one who can give him a real fight, as an equal, with an actual chance, is Olmert," Caspit said. "Netanyahu is a strong prime minister and if he really wanted he could pass a budget. But he doesn't really want to. What he wants is to pre-empt Olmert's comeback, catch his opponents off guard and steal a new term before it's too late."

Despite the call for early elections, most Israelis believe the next government will have the same make-up as the current one, according to a poll published Wednesday.

A Dahaf survey showed that 64 percent of those polled said the next coalition will have the same composition of parties, while 62 percent said the government's policies will also remain unchanged.

The poll surveyed 440 Israelis and had a margin of error of 4.7 percentage points.