Ariel Sharon underwent five hours of emergency brain surgery Friday that doctors said successfully stopped a hemorrhage and relieved swelling inside his skull. Officials said his condition showed "significant improvement" but experts said the prognosis remained dire.

Sharon's chief surgeon told The Associated Press it was too early to assess how much damage the prime minister suffered after three similar operations in two days. That determination will have to wait until at least Sunday, when doctors plan to wean him off the drugs that are keeping him in a state they described as a medically induced coma.

Acting Prime Minister Ehud Olmert took calls Friday from Secretary of State Condoleezza Rice and Egyptian President Hosni Mubarak, a sign that the Israeli government was moving ahead without its hard-charging leader. Sharon's Kadima Party said it would rally around Olmert, and a new poll showed Kadima emerging victorious in March 28 elections under his leadership.

Palestinian leaders, holding a parliamentary election of their own Jan. 25, said they were in touch with Israeli officials about Sharon's condition. "We are closely monitoring the situation," Palestinian negotiator Saeb Erekat said.

The White House declined to speculate on how Sharon's illness could affect the peace process.

"The United States view of the Middle East is that the desire for progress and peace runs wide and deep," spokesman Trent Duffy said. "The president continues to pray for the recovery of Prime Minister Sharon."

Rice, who canceled a six-day trip to Indonesia and Australia, told Olmert that "every U.S. citizen, from the president to the last citizen, are praying for Sharon's health," according to Olmert's office.

"Despite the difficult situation, this evening Israeli citizens have a little more hope," Olmert told her.

But experts not involved in Sharon's care said he may have fallen into a coma by himself as a result of the massive hemorrhagic stroke he suffered Wednesday while en route to the hospital. In that case, Sharon might not regain consciousness when the drugs are withdrawn. Interaction with the patient is required to assess some aspects of brain function.

As the Sabbath descended on the Jewish state Friday, the vigil for the 77-year-old Sharon became increasingly somber. The Israeli leader's aides held a grim vigil at the hospital and elder statesmen Shimon Peres said he was "very worried" about his old friend.

At Hadassah Hospital in Jerusalem, Sharon's sons, Omri and Gilad, camped out in a room next to their father's at the neurological intensive care unit. Sephardic Chief Rabbi Shlomo Amar took to the airwaves to advise Israelis which psalms to read for Sharon. "All that is left to do is to pray," Israel's other chief rabbi, Yona Metzger, said.

Shmuel Rabinovitch, rabbi of the Western Wall, said he received dozens of e-mails praying for Sharon's health that he printed out and stuck in the cracks of the holy site. Callers from as far away as Venezuela and the United States asked for advice in praying for Sharon, he said.

Sharon was rushed into the operating room Friday morning after a brain scan indicated rising cranial pressure and further brain hemorrhaging.

Hospital director Dr. Shlomo Mor-Yosef said the new surgery Friday helped stabilize Sharon's condition. "Part of the blood clots that remained after the first operation were drained," he said. "At the end of the operation, there is no active bleeding and the intracranial pressure has returned to normal."

Mor-Yosef said a comparison of brain scans before and after the surgery showed "significant improvement," but he did not elaborate.

The chief neurosurgeon operating on Sharon, Dr. Felix Umansky, said he came through the surgery well but was likely to have suffered damage.

"There is always some damage when you have cerebral hemorrhage," he said in a telephone interview. "We cannot assess the damage because he is under anesthesia all the time. We need to wait and see what will happen once we reduce the medication which keeps him under sedation."

Hospital officials said Sharon would remain in the medically induced coma until at least noon Sunday to give him time to heal.

It was unclear whether the new bleeding was from a second rupture of the same blood vessel that caused the original massive stroke or a break in another vessel, which would constitute a new stroke. New bleeding from the stroke-causing blood vessel in the first few days after a hemorrhagic stroke is a common cause of death in patients. Another chief killer of such patients is swelling of the brain.

Independent doctors said Sharon's chances for recovery were slim, and Sharon's aides said they were working on the assumption he would not return to work.

"One feels slightly more positive about the outcome because some of the problems have been able to be reversed, but the underlying problem remains. He still had further bleeding and that doesn't change the prognosis, which still looks dire," said Dr. Anthony Rudd, a stroke specialist at St. Thomas' Hospital in London.

Noting that a CT scan shows the structure — not the function — of the brain, Rudd said the improvement that Sharon's doctors referred to likely applies to the reduction of swelling seen in the earlier scan.

The surgery Friday followed two operations Sharon underwent Thursday after he suffered a massive brain hemorrhage as he rode in an ambulance to the hospital from his ranch in southern Israel. That operation was interrupted as Sharon underwent testing, then resumed after the test results were analyzed.

Sharon's grave condition threw Israeli politics into flux less than three months before national elections. Israeli officials said the elections would proceed as scheduled regardless of Sharon's fate.

The new poll released Friday showed Kadima would still sweep the vote, even without Sharon, who formed the party after bolting the hardline Likud last year following Israel's withdrawal from the Gaza Strip. Kadima's platform seeks a compromise for peace with the Palestinians.

The poll published in the Yediot Ahronot daily Friday found that an Olmert-headed Kadima would win 39 of 120 parliament seats, slightly fewer than the party polled under Sharon but enough to lead the next government.

The poll of 500 people was taken Thursday and had a margin of error of 4.4 percentage points. Some pollsters said the results might be influenced by sympathy for Sharon and could change during the campaign.

The poll showed Peres would net 42 seats as Kadima leader, but analysts said it was unlikely he would be chosen to lead the party. Peres met with Olmert on Friday but did not give details of their talk.

"We will know how to continue Israel's policy ... to continue Ariel Sharon's policies," Peres said.

As Israelis rushed to prepare for the Sabbath, many were fatalistic.

"It's very sad that he's going," Itzik Gordon, a 48-year-old contractor, said of Sharon. "He was a real leader, from the establishment of the state until now."