Former Israeli prime minister Binyamin Netanyahu, who quit the cabinet this month to protest Israel's withdrawal from the Gaza Strip, announced his candidacy for the Likud Party leadership Tuesday in a direct and highly personal challenge to Prime Minister Ariel Sharon.

"I intend to lead the party to victory in the coming elections and form the next government," Netanyahu said during a news conference at which he gave a harsh critique of Sharon, Likud's current leader.

"He abandoned the principles of the Likud," said Netanyahu, 55, who was prime minister from 1996 until 1999, when he was badly beaten by Labor Party leader Ehud Barak. "He chose a different path, the path of the left. We have to restore to the Likud and the state the principles that Sharon trampled on."

The announcement has been expected since Netanyahu resigned Aug. 7 as finance minister to register his opposition to Israel's withdrawal from 21 settlements in Gaza and four in the northern West Bank, a plan he voted for several times in the cabinet while calling unsuccessfully for a public referendum to block it.

Israel's elections must be held before November 2006, and many political analysts here say voting will be held next spring given the tumultuous state of Likud, the dominant conservative party. Netanyahu's first comments as a candidate gave a flavor of the bitter struggle ahead between two men who deeply dislike each other. A day earlier, Sharon told Israel's Channel 10 television that "Netanyahu is a man who gets stressed."

"In any situation of pressure, he gets stressed immediately," Sharon said in the interview. "He panics and loses control. I've seen him like that more than once, many times."

A showdown within Likud for the party leadership, which could come as soon as November, would be the next step in a realignment that is taking place along generational lines within Israel's highly factional political system, precipitated by the Gaza withdrawal.

Once a standard-bearer of the Israeli right as a staunch supporter of settlements and a skeptic of the Palestinian peace process, Sharon, 77, has alienated many of his former followers by pulling out of Gaza.

In the months before what he called disengagement, Sharon turned to his old friend and political rival Shimon Peres, head of the more dovish Labor Party, to shore up his government. The two men have been active in public life here since before Israel's founding in 1948.

Some analysts say Sharon and Peres may break from their parties and form a new alliance with Yosef Lapid, head of the secular, centrist Shinui Party, that could win enough seats in Israel's parliament to form a government. Sharon could also form a new party with just his Likud supporters, splitting a movement that now controls one-third of the 120-seat parliament.

"The big question is what will Sharon do," said Gabriel Sheffer, a political science professor at Hebrew University in Jerusalem. "He's playing his cards close to his chest. There are pluses and minuses to forming a new party. Right now, I think, it's an open question.

"The enmity between these two people is very great," Sheffer continued. "If Netanyahu loses, I still think he would serve in a Sharon government. If Sharon loses, he would not serve under Netanyahu."

While surveys say Sharon would lose a Likud primary to Netanyahu, they also show him faring far better than his rival among the public at large in a general election. A shrewd tactical politician, Sharon defied a party referendum in which most members opposed his plan to unilaterally withdraw from Gaza. Yet the evacuation concluded far more swiftly than military officials had predicted, and opinion polls suggest that a majority of Israelis favor withdrawing from additional settlements in the West Bank.

The Likud central committee, a 3,000-person caucus considered more conservative on issues of peace and settlements than its broader membership, plans to decide next month whether to move up party primaries to oust Sharon. A vote to do so could be held as early as November and would mark the first time a party sought to topple its chairman while he was serving as prime minister. Netanyahu is the third and by far the most powerful candidate to announce a challenge to Sharon for the party leadership.

Binyamin Netanyahu, who resigned as finance minister this month, has rallied opposition to Prime Minister Ariel Sharon's pullout from Gaza.