UNITED NATIONS — The General Assembly is preparing to approve a resolution that would endorse a United Nations report calling on both Israel and the Palestinians to investigate possible war crimes in the Gaza Strip within three months.

The assembly began discussing the nonbinding resolution, introduced by about 20 Arab League members, including Iraq, on Wednesday, but with about 50 nations scheduled to speak, a vote was not likely until Thursday. Given the widespread support for the Palestinian cause and broad criticism of Israel, passage of the measure seemed assured.

Some members of the European Union were threatening to abstain, however, holding out for changes. One issue was wording that would require Secretary General Ban Ki-moon to work with the Security Council on additional action; another was the resolution’s full endorsement of a decision last month by the United Nations Human Rights Council to adopt the report completely, diplomats said.

The 575-page report, which was released in September, found evidence of war crimes committed by both the Israeli Army and Hamas fighters during the Gaza war last winter. The report was researched and written by a fact-finding mission created by the Human Rights Council and led by Richard Goldstone, a South African judge and a former war crimes prosecutor for Rwanda and the former Yugoslavia.

It was unclear on Wednesday whether some European Union members would follow through on the threat to abstain. Ambassador Anders Liden of Sweden, speaking as the union’s current president, said that its members remained concerned about the deteriorating humanitarian and human rights conditions in the territories occupied by Israel.

Israel maintains a blockade around Gaza, preventing the entrance of hundreds of millions of dollars of material pledged by numerous governments, including the United States, to rebuild after the extensive destruction caused by the war.

The draft resolution in the General Assembly condemns “all targeting of civilians.” It proposes a three-month deadline for Israel and Hamas to take steps toward independent investigations of war crimes. The demand would keep the report alive, but the resolution stands little chance of moving to the Security Council for enforcement action. The United States has a history of vetoing any move critical of Israel. But other permanent members also dislike the idea of the Goldstone report becoming a precedent, diplomats said, with China thinking of its control over Tibet and Russia its actions in Chechnya and elsewhere.

The speeches in the General Assembly on Wednesday echoed the arguments that have erupted since the report was issued Sept. 15. Israel said its actions were determined by the need to defend itself against rockets fired by Hamas into Israeli cities, which it called terrorist attacks.

“The report ignores the reality of terror activity and the complexity of military challenges in fighting terrorists in urban warfare,” Gabriela Shalev, the Israeli ambassador, told the General Assembly. Ms. Shalev argued that the report essentially denied Israel’s right to self-defense. “If Israel is asked to make concessions for peace, we must be assured of the right to defend ourselves,” she said.

Israel’s critics said that as the occupying power it had a special responsibility to protect civilians and that many targets that were destroyed, including a flour mill and a sewage treatment plant, had no evident military value.

Maria Luiza Ribeiro Viotti, the Brazilian ambassador, said Israel had to respect international law in the process of defending itself, “especially in situations of asymmetrical warfare in densely populated areas, where civilians are likely to be much more exposed to the effects of military action.” She also echoed many ambassadors when she said that rigorous investigations by both sides, with monitoring by the international community, would enhance peace negotiations.

“There must be no room for vengeance, which only brings more violence, but for accountability, which brings reparation, and therefore, peace,” she said.

The United States was not among the nations scheduled to address the General Assembly.

On Tuesday, the House of Representatives voted 334 to 36 to condemn the Goldstone report as “irredeemably biased and unworthy of further consideration or legitimacy.”

Judge Goldstone issued an open letter to the House Committee on Foreign Affairs, listing 16 instances in which he said the House resolution had distorted his report. While the House had every right to weigh his report, he wrote, the resolution included “serious factual inaccuracies and instances where information and statements are taken grossly out of context.”