JERUSALEM — Benjamin Netanyahu’s chief rival announced Wednesday that he had failed to form a new government, dashing his hopes of toppling the longtime Israeli prime minister and pushing the country closer toward an unprecedented third election in less than a year.

The announcement by Benny Gantz, leader of the centrist Blue and White party, prolongs the political paralysis that has gripped the nation for the past year. It also provides a new lifeline for the embattled Netanyahu, who is desperate to remain in office as he prepares for an expected indictment on corruption charges, possibly as early as Thursday.

Gantz, a former military chief, was tapped to form a government last month after Netanyahu failed to cobble together a coalition in the wake of inconclusive September elections.

But during four weeks of intense negotiations, Gantz was unable to muster the support of a required 61-member majority in the 120-seat parliament by Wednesday’s midnight deadline.

Addressing reporters, Gantz accused Netanyahu of scuttling attempts to form a broad-based unity government between their parties.

“He should have come to terms with the fact that the outcome of the elections required him to negotiate directly, with no blocks or barriers,” Gantz said angrily.

“Most of the people chose a liberal unity government headed by Blue and White,” he added. “Most of the people voted to weaken the power of extremists, and most of the people voted to go on a different path from that of Netanyahu in recent years.”

Under Israeli law, parliament now enters a 21-day period where any lawmaker can try to muster a 61-seat majority and become prime minister.

That means both Gantz and Netanyahu will continue their efforts to find coalition partners and to explore the possibility of a unity government. Dark-horse candidates may also emerge. If they fail, the country would be forced to hold another election in March.

“These are 21 fateful days in which Israeli democracy will be challenged by the most important test,” Gantz said. He vowed to try to find a way to pull Israel “out of the total paralysis that was forced upon us.”

Gantz’s Blue and White is the largest party in parliament, with 34 seats, just ahead of Likud’s 33, meaning the two men together could control a majority. But during weeks of talks, they could not agree on the terms of a power-sharing agreement, including who would first be prime minister and what would happen if Netanyahu is indicted.

Opinion polls have indicated a new election would deliver similar results to September’s inconclusive vote, signaling additional months of horse-trading and uncertainty.

The race, however, could be shaken up by the expected indictment of Netanyahu in a series of corruption cases. Channel 13 TV reported that Attorney General Avichai Mandelblit has decided to file fraud and breach of trust charges and an announcement could come as soon as Thursday. There was no confirmation from the Justice Ministry.

Netanyahu is desperate to remain in the prime minister’s post, where he would be best positioned to fight the charges and seek immunity from prosecution from parliament. With the exception of prime minister, Israeli law requires public officials to resign if charged with a crime.

Gantz has ruled out a partnership with Netanyahu at a time when he is facing trial, but has said he has no objections to partnering with Likud if it is led by someone else.

Wednesday’s crisis was triggered by Avigdor Lieberman, leader of a small secular, ultranationalist party who has emerged as Israel’s political power broker.

Neither Gantz nor Netanyahu was able to form a majority government without Lieberman’s support. But on Wednesday, Lieberman said he would not endorse either candidate.