THE Israeli Labor Party ended its fifth congress here yesterday, still struggling to find an identity and a leader capable of winning its first decisive election victory in nearly 20 years.But the sharp exchanges that marked the three days of debate heightened the divisions that have plagued the party, as it languishes at almost its lowest ebb ever in the opinion polls. Highlighting the crisis, some prominent left-wing figures left the congress still threatening to resign from the party, after their attempts to impose a more dovish peace policy and to detach the party from its traditional trade union underpinnings were defeated by mainstream delegates. By an overwhelming majority, the congress voted to maintain Labor's traditionally socialist economic and social outlook, while also backing the leadership's refusal to countenance a Palestinian state. At the same time, they approved policies to relax the state's bureaucratic control over the economy and again endorsed the principle of territorial concessions in order to make peace with Palestinians and Syrians. (Shamir in Boston, Page 7.) The debates that preceded adoption of this compromise platform, which Labor will carry to elections due next year, offered ample opportunity for what deputy party leader Yitzhak Rabin called "the combination of many voices, in contradiction with each other, that come from the Labor Party without making clear cut the differences between Labor and [the ruling] Likud on the one hand, and between Labor and the extreme left." While a minority of left-wing doves urged the congress to take a softer line on peace negotiations with Israel's Arab neighbors, for example, by not ruling out the possibility of a Palestinian state, the policies eventually approved shared much in common with the Likud government's current approach to the peace talks. "I'm not sure the Israeli people are sure of the differences between us and Likud," complained Hagai Merom, one of the doves in Israel's parliament, or Knesset. "The message is not clear enough, and people don't understand what the Labor Party believes in." The key differences, insists party leader Shimon Peres, are that Labor favors a "territories-for-peace" deal that Likud rejects, and also proposes a one-year freeze on all Jewish settlement activity in the occupied territories. Opinion polls show that these policies enjoy wide support. "The people like our ideology, and agree with our approach," says Susan Hattis Rolef, editor of the Labor magazine Spectrum. "The problem is that they believe the Likud will implement it." In the wake of a 20-year decline in electoral support, the Labor Party now commands the loyalty of only 22 percent of the electorate, as against 37 percent for the Likud, according to a poll conducted earlier this month. Though Mr. Peres shrugs off those results as "a passing cloud" after the Madrid peace talks, his longtime rival, Mr. Rabin, says, "There is no doubt they represent a trend," and blames "the lack of credibility in the Labor image ... because there is no clear cut authority in the party." After four consecutive elections in which Peres has failed to win enough votes to form a Labor government, many other party members blame their leader. "The crisis of the party is a crisis of personal leadership," says Knesset member Shimon Shitreet. This week's congress introduced a new system of primaries to elect the party leadership, to be put into effect next February, which will give each Labor member a vote. But it is by no means clear that Rabin, generally considered more electable than Peres, will emerge victorious. At the same time, argues Danny Bent Simon, political analyst for the pro-Labor newspaper, Davar, "the splits in the party are not just between Peres and Rabin. They are between young and old, between economic conservatives and liberals, between hawks and doves. The real question is whether there will be a real identity after this congress, or the usual supermarket of ideas from left to right." At a deeper level, Labor's travails are rooted in historical, ethnic voting patterns. While it relies on Ashkenazi Jews of European origin for 70 percent of its support, Likud counts on the generally more hawkish Sephardic Jews from the Middle East and North Africa to back its policies. "The Sephardic voters are a majority and increasingly so," says Hebrew University Politics professor Peter Medding, "which only makes Labor's task harder." Peres says he is confident that "there will be new audiences that will decide the next elections," and he plans to appeal directly to them - the Israeli Arabs who have traditionally supported the crumbling Israeli Communist party, and the 300,000 recently arrived Soviet Jews. None of the current opinion polls, however, suggest Labor can garner enough support among these groups to offset its lack of credibility elsewhere.