Israeli Prime Minister Ariel Sharon resigned Monday from the Likud Party he helped build into one of the country's most influential political movements, setting in motion events that will lead to spring elections and a far-reaching realignment of Israel's fractious political system.

Sharon submitted a resignation letter to the Likud central committee chairman, Tzahi Hanegbi, making official his departure from the party he has twice led to victory in national elections. Hours later, Israel's parliament voted overwhelmingly to dissolve itself in a move intended to lead to new elections by the end of March, about eight months ahead of schedule.

By Monday evening, 13 of Likud's 40 members of parliament had joined Sharon in a new centrist party, tentatively named National Responsibility. A number of them gathered at Sharon's office to hear from the prime minister, who outlined a political program focused on the U.S.-backed peace plan known as the "road map" and tackling Israel's rising crime and poverty rates.

Likud flourished with Sharon as one of its leaders as a proponent of the idea of a Greater Israel that encouraged Jewish settlement of the West Bank and Gaza Strip, seized in the 1967 Middle East war. Sharon went against Likud doctrine in the evacuation of settlements and soldiers from the Gaza Strip earlier this year, and his departure now reflects the sentiments of an Israeli electorate that favors a resolution to the conflict with the Palestinians even if it means further territorial concessions. With the Gaza evacuation, the key question turns to the West Bank and whether to yield additional land there that could be part of a future Palestinian state.

"In its present form, the Likud cannot lead Israel toward its national goals," Sharon said at an evening news conference. "Staying in the Likud means wasting time on political struggles, rather than acting on behalf of the state."

Sharon suggested that he would take steps to consolidate Israel's presence within the established Jewish settlement blocs that he says will remain part of Israel under any peace agreement. The final status of the settlements, he said, would be addressed in the road map's last phase and could mean the removal of some of them.

"The citizens of Israel deserve leadership which acts, first and foremost, for the good of the public, and not for the narrow political interest," Sharon said.

Sharon is the first sitting prime minister to leave his party. His move came about, close aides said, because he believed he could no longer accomplish his goals as Likud's leader.

Sharon alienated much of Likud's hawkish base by evacuating the Gaza settlements, a move he said was needed to establish defensible frontiers and preserve the viability of Israel's Jewish majority at a time of a fast-growing Palestinian population. But Palestinian leaders say Sharon has done little since then to ease Israel's 38-year occupation of the West Bank and has not shown any inclination to begin negotiations under the road map. Sharon says the talks must be preceded by a more effective Palestinian crackdown on armed groups at war with Israel.

Several advisers said Sharon's decision, reached after weeks of conversations with Likud members, was based on practical considerations as the 77-year-old prime minister prepares for what could be his last election. Israeli political analysts say Sharon, the brash former general and driving force behind Israel's long military involvement in Lebanon, might also have his legacy in mind.

"He really believes, whether ideologically or for reasons of realpolitik, that the best way to secure Israel's future is to create fixed, permanent borders, unilaterally," said David Hazony, editor in chief of Azure, a political journal published by the Shalem Center in Jerusalem. "I think he feels that he can't trust the people that come after him, and he has made no attempt to groom the next generation of political leaders. He feels that anything that ought to happen should happen while he's running the show."

Although Sharon has grown more popular among Likud pragmatists, aides said he became convinced that he would never have the party's support to take steps demanded by the road map, which calls on Israel to freeze settlement construction, or to carry out further unilateral withdrawals. Among those who did not join Sharon is Shaul Mofaz, his defense minister, who announced Monday that he would seek the Likud leadership.

"His clear intention is to proceed with a political process with the Palestinians," a senior Sharon adviser involved in the discussions said of the prime minister. "The current composition of the Likud meant paralysis. He needs space and freedom and support to achieve what he wants to do."

Although broadly popular with the Israeli public, Sharon is taking a risk by leaving Likud, which he helped transform from a group of mostly marginal hawkish parties in 1973 into a coalition that four years later unseated the founding Labor movement in national elections. He gives up the Likud name, financial resources and television advertising time, which in Israel is tied to the number of seats a party holds in parliament. Sharon called Monday for members of the rival Labor Party to join him.

Likud attracted low-income Jews of North African and Middle Eastern descent, who felt ignored by the mostly European-born Labor leadership, as well as religious nationalists who supported Jewish settlement in the territories. Sharon was once the chief political patron of the settlement movement, which now considers him a foe.

Israeli political analysts say Sharon is counting on the continuing loyalty of some Likud voters and fresh support from Israeli doves who backed his Gaza withdrawal but would never, as a matter of principle, vote for a Likud candidate. A recent opinion poll published in Yedioth Ahronoth, Israel's largest daily newspaper, showed that a new party under Sharon would win 28 seats in the 120-member parliament, with Labor also taking 28, a seven-seat gain.

The same poll showed that a Likud led by Sharon's chief rival, Binyamin Netanyahu, would lose more than half of its current 40 Knesset seats in voting that included Sharon's new party and others. That would make Likud, which now controls a third of the Knesset, the third-largest party in parliament.

Gideon Ariel, a Likud central committee member who opposes Sharon, described as "a bunch of spin" the polls showing the party foundering without Sharon. Although Likud will likely lose seats in the next elections, he said, the party will grow more popular in the settlement of Maale Adumim east of Jerusalem where he lives.

"It was very uncomfortable for me to promote Likud, the nationalist party, when Ariel Sharon was pushing anti-nationalist policies," Ariel said. "We are now relieved of his punishment -- his pretending that he is a right-wing politician when he is really favoring center-left policies."

Researcher Samuel Sockol contributed to this report.

Israeli Prime Minister Ariel Sharon said that "staying in the Likud means wasting time on political struggles." The prime minister said Likud "cannot lead Israel toward its national goals."