Abbas said he would give Hamas until Thursday to agree to the plan or face a national referendum. Abbas had initially given Hamas until Tuesday to respond to the ultimatum, but decided to give the group additional time after consulting with the powerful PLO executive committee.
Abbas wants to hold the nonbinding vote to put pressure on the Hamas-led government to accept the plan, which calls for a Palestinian state alongside Israel, implying recognition of the Jewish state. Hamas, which is committed to Israel's destruction, has demanded changes to the proposal and said it will boycott the referendum.
During Tuesday's meeting, the PLO Executive Committee endorsed the document and authorized Abbas to call his referendum, said Yasser Abed Rabbo, a senior Palestinian official. He said Abbas will not accept any changes to the document.
"President Abbas has informed the PLO leadership that he is going to prepare for the referendum by the end of the week and he will announce this at a press conference before the weekend," Abed Rabbo said. "We are giving enough time, about three days, for our brothers in Hamas to reconsider their position."
The referendum would be held 40 days after the announcement. Abed Rabbo said negotiations with Hamas could continue until the day of the vote.
Hamas officials welcomed the offer to extend an ongoing "dialogue" over the document but said they remained opposed to any deadlines.
"We still have a chance to make this dialogue a success," said Prime Minister Ismail Haniyeh of Hamas at a Cabinet meeting in Gaza City. "Therefore we ask for more meetings and more dialogue and that we don't use the language of days and time as a threat."
Hamas, Abbas' Fatah movement and smaller Palestinian factions have been holding sporadic talks on the proposal for nearly two weeks since Abbas issued his ultimatum. Haniyeh and Abbas spoke by telephone for more than an hour late Monday in a last-ditch effort but failed to reach a deal.
During the discussion, Abbas angrily demanded that Haniyeh take a more statesmanlike approach.
"I hope, brother Ismail Haniyeh, that you act as a head of a government that is responsible for all Palestinian people and not as a member of a political party, mouthing party slogans," Abbas told Haniyeh, according to an account of the conversation by Abed Rabbo.
Abbas has been involved in an increasingly bloody power struggle with Hamas since the Islamists defeated Fatah in legislative elections early this year. Abbas, elected separately last year and who wields significant power, has taken steps to curb Hamas' authorities.
In the latest violence, rocket propelled grenades were fired Tuesday at a security compound in the Gaza Strip, moderately wounding three maintenance workers, officials said.
The compound houses the headquarters of the Preventive Security agency, which is loyal to Abbas and has been at the center of the infighting. Hamas has accused the agency of being behind attacks against the government's new private militia.
Fatah officials accused Hamas of being behind Tuesday's attack. Haniyeh called the incident "regrettable" and called for restraint by all sides.
Abbas' referendum plan calls on the Palestinian public to endorse a plan formulated by senior Fatah and Hamas prisoners held by Israel. But Hamas' exiled leadership, which has the final say in policy decisions, has refused to endorse the plan, officials say.
Abbas believes the plan provides a way to lift crushing economic sanctions against the Palestinians and to enable him to resume peace talks with Israel.
A vote could deeply embarrass Hamas. Polls show the prisoners' document would win broad approval. Hamas won January elections in a landslide against Abbas' Fatah, but government inefficiency and corruption were the main issues, not policy toward Israel.
A new survey released Tuesday showed 77 percent of Palestinians support Abbas' call to hold a referendum on the proposal, and the same percentage would vote in favor of the proposal. The survey of 1,200 Palestinians was conducted by Bir Zeit University in the West Bank and had a margin of error of 3 percentage points.
The same poll showed willingness to vote for Hamas declined to 37 percent from 50 percent a month earlier. Voting for Fatah was stable at 37 percent.
Hamas opposes the existence of a Jewish state in an Islamic Middle East and has rebuffed Western demands to recognize Israel, accept previous peace accords and renounce violence. The West cut off aid to the Hamas-led government, leading to a financial crisis.
The Palestinians have never held a referendum before, and officials said the vote would not be binding. But passing the referendum could give Abbas an important boost in his standoff with Hamas.
While the financial crisis has left the government unable to pay the salaries of tens of thousands of civil servants, Israeli military officials said Tuesday that Hamas has managed to smuggle hundreds of thousands of dollars into the Gaza Strip in recent weeks.
The money has enabled Hamas to sustain key operations, including charitable activities and operations of its new 3,000-member security force, the officials said.
Asked about the smuggling, government spokesman Ghazi Hamad did not deny it. "We will look for money everywhere and every place. That is our right," he told Israel's Army Radio.