Labor Party Chairman Shimon Peres today overwhelmingly turned back a challenge by former prime minister Yitzhak Rabin for the party leadership and the right to oppose Prime Minister Menachem Begin in next year's elections.

Peres' margin of victory -- slightly more than 70 percent of the 3,019 delegate votes counted in the party's annual convention -- is expected to give him a much freer hand in shaping the opposition party's challenge to Begin and in forming a government if the Labor Party wins next year's parliamentary election.

The one-sided outcome today over-shadowed the bitter party factionalism that had arisen from Peres and Rabin's long rivalry and appeared to put Labor on a sounder footing than it has been on in years.

Immediately after the votes were counted in Tel Aviv today, Peres, in a move clearly intended to heal the deep divisions within the party, declared, "I would like to shake the hand of Yitzhak Rabin, and through him shake the hands of all those comrades who voted for him out of complete freedom."

Observers said it was the first time in four years that Peres and Rabin, who are barely on speaking terms, had shaken hands. Peres had replaced Rabin as party chairman in 1977 when Rabin, then prime minister, became involved in a scandal over a bank account he and his wife had in the United States in violation of Israeli currency regulations.

Whether the decisive outcome of the vote, coupled with Peres' conciliatory gesture, would be enough to unite the party beyond the euphoria of a festive political convention remains to be seen.

Rabin repeatedly has said that even if he were defeated in the leadership race, he would insist that his and Peres' "camps" remain intact and separate within the party. He noted that when he defeated Peres for the leadership in 1974 he permitted Peres' faction to serve in his government.

It was while Peres served as Rabin's defense minister that their rivalry deepened, with Rabin accusing Peres of undermining him.

Peres' victory margin today was important. Had it been less, Rabin's faction could have blocked Peres' appointments to the party's parliamentary election slate.

Moreover, Rabin could have had considerable influence on the makeup of a future Labor Party Cabinet.

In a press conference today, Peres was noncommittal about including Rabin in his government.

"I don't intend to make any specific declaration about any person," he said.

"I do not exclude Yitzhak Rabin, but names will be announced together once we announce the leading team of the party."

Rabin repeatedly has said his "personal inclination is not to serve under Peres," but that if he did he would serve only if he felt he could be a "loyal minister."

Peres said today, "We are now beginning the fight, and it will be a very difficult fight in changing the outlook of this country and giving it back its pioneering nature."

Rabin said, "I accept and honor the decision of this convention." He added that he hoped the party would emerge "united and strong . . . and ready for the contests next year."

The parliamentary election is scheduled for November, but it could come sooner if Begin's rightist Likudled government loses one of the increasingly frequent and close no-confidence votes.

Ironically, national polls show that the Labor Party, which ruled Israel from 1948 until Begin won an upset victory in 1977, might be better off with Rabin as the candidate.

Rabin has a 24 percent approval rating, compared to 22 percent for Peres and 12 percent for Begin. Rabin is frequently described by voters as statesmanlike and trustworthy, while Peres is often spoken of as the quintessential professional party politician and backroom manipulator.

But Rabin's failure to capture more than 875 delegate votes, compared to Peres' 2,123, demonstrated who was more adept at building a power base in the party following the trauma of 1977, when Rabin resigned the premiership following the scandal over the illegal bank account.

Peres succeeded Rabin in the party leadership but was defeated by Begin in the national election five weeks later. Since then, Peres has been quietly rebuilding the shattered party while building his own base with the kind of political expertise he developed in a lifetime of Labor Party activism.