Israel officially opened its election season on Monday as parliament dissolved itself and scheduled a vote for January, plunging the country into a vicious, three-month political campaign.

Israeli leaders launched harsh attacks on one another during a long parliamentary debate that preceded the vote to dissolve parliament that passed late unanimously late Monday night, setting the parameters for what is likely to follow in the campaign. Prime Minister Benjamin Netanyahu boasted of his achievements, while the opposition heckled and insulted him mercilessly.

Netanyahu announced last week that he was calling early elections, months ahead of schedule. The immediate reason for the vote is his coalition government's inability to pass a budget by a Dec. 31 deadline. With the economy slowing, the government would have been forced to make steep cutbacks unpopular with voters.

But after leading a remarkably stable coalition for nearly four years, Netanyahu also appears to have sensed that the time is ripe to win a new term. Netanyahu's Likud Party is leading in most opinion polls, and his opponents remain divided and disorganized.

Parliament approved Netanyahu's proposal for elections on Jan. 22. Elections had been scheduled for October 2013.

Yet Netanyahu still faces some areas of vulnerability, including the uncertain economic situation, a failure to advance peace efforts with the Palestinians and his rocky relations with U.S. President Barack Obama.

In an address to parliament ahead of Monday's vote, Netanyahu boasted of a series of accomplishments under his leadership. He emphasized that Israel's economy grew while most other countries suffered setbacks, took credit for the relative decline in Palestinian attacks against Israelis, and said he put Iran's nuclear program on the global agenda to the point where the country was now under crippling economic sanctions.

"In less than 100 days the people of Israel will determine who will lead it," Netanyahu said. "Who will lead it against the biggest security challenges we have known since the state was founded, who will lead it against the worst financial crisis the world has known in the past 80 years."

"All those who belittle the threat of a nuclear Iran are not worthy of leading Israel even one day," he added.

Netanyahu was repeatedly interrupted by shouts and boos by opposition lawmakers.

In a separate speech, opposition leader Shaul Mofaz countered with a blistering attack Netanyahu's shortcomings.

He said that by doing nothing on peace with the Palestinians and continuing settlement building in the West Bank, Netanyahu was making the areas inseparable and bringing Israel ever closer to being a binational state evenly divided between Jews and Arabs. Without the West Bank, Jews make up a 75 percent majority of Israel.

The Palestinians claim all of the West Bank, captured by Israel in the 1967 Mideast war, as part of a future state. They say continued Jewish settlement in the territory make it impossible to partition the land into two states. Throughout Netanyahu's term, the Palestinians have refused to negotiate, saying settlement construction must first be halted. The international community has nearly universally condemned the settlements.

Mofaz also blasted Netanyahu for undermining Israel's relations with the United States through repeated quibbles with Obama, leaving the widespread impression that he is supporting Republican challenger Mitt Romney in the upcoming U.S. elections.

"Where is your responsibility to Israel's fate with its greatest and almost only ally, the United States? Why are you aggressively interfering in the democratic elections in the United States? Why? What need was there to do that?" Mofaz asked, as Netanyahu listened impassively.

Opinion polls have forecast that the Likud would win roughly 29 seats in the 120-member parliament, making it the largest single party and putting Netanyahu in position to form a new coalition government. The polls predict the nationalist and religious parties that dominate his current coalition will likely control a majority of seats in the next parliament as well.

Netanyahu could be vulnerable if the focus of the campaign veers from diplomatic issues to social ones. The government has come under fire for the growing gap between rich and poor.

The dovish Labor Party has seen its support grow after mass social protests against the country's high cost of living drew hundreds of thousands to the streets in the summer of 2011. Labor leader Shelly Yachimovich tends to favor a strong government safety net and is running a campaign primarily on jobs and the economy.

In a setback for Netanyahu, one of his most popular Cabinet ministers announced late Sunday that he was leaving politics. Moshe Kahlon has been the Likud minister most close to working-class voters, and in his role as communications minister, has won accolades for taking on Israel's powerful wireless cartel and forcing them to lower prices by introducing new competitors.

Hebrew University political scientist Gayil Talshir said Kahlon's departure could hurt Likud's standing with its base of Mizrahi Jews, those of Middle Eastern descent. Kahlon, the son of Libyan immigrants, grew up in a hardscrabble town and is one of the few Mizrahi politicians in the upper echelons of the Likud.

"For the first time in an election, the economic and social issues are going to be on the top of agenda. And Kahlon could have helped with this, so it's a very, very big loss," she said.

Yachimovich is sure to capitalize on Netanyahu's image as a cold advocate of free markets and capitalism. Mofaz, the opposition leader, has seen his Kadima Party slip badly in the polls, while a new centrist party led by former TV anchorman Yair Lapid remains something of an unknown. Pressure is on the three to unite into a superparty that could challenge Likud.

Another issue that could hurt Netanyahu is the unresolved status of draft exemptions granted to ultra-Orthodox Jewish males.

Earlier this year, the Supreme Court ordered the exemptions to stop and that alternative legislation be drafted. Mofaz even briefly joined the government in an attempt to find a solution, to no avail.

Israel's secular majority, which has to serve compulsory military service, resents these exemptions. Secular Israelis are also alarmed by ultra-Orthodox efforts to segregate the sexes in public, their widespread reliance on state handouts, and a school system that teaches religious studies but few skills for the work world.