Doctors said Thursday that Israeli Prime Minister Ariel Sharon will be kept in a coma-like state for up to three days to prevent further damage from a massive stroke. His sons held a bedside vigil and state media broadcast mournful songs.

Hadassah Hospital's switchboard was flooded with get-well messages and the nation's top rabbis called on Israelis to rush to synagogues and pray for the 77-year-old ex-general, whom many saw as the best hope for peace with the Palestinians.

Sharon's deputy, Ehud Olmert, tried to convey a sense of stability while serving as acting prime minister, but Sharon's dramatic downturn left Israelis fearful.

The Web site of the respected Haaretz daily quoted hospital officials as saying Sharon suffered vast brain damage.

But Dr. Shlomo Mor-Yosef, Hadassah Hospital director, sought to quash widespread rumors that the prime minister was brain-dead. Sharon's pupils were responding to light, "Which means the brain is functioning," he told reporters.

"We are fighting for the life of the prime minister, with no compromise," he said.

Dr. Zeev Feldman, a neurosurgeon at Israel's Tel Hashomer Hospital who is not involved in Sharon's treatment, said the test results appeared encouraging.

"I think this is good news. This information that the prime minister is reacting and they got reactions from him to stimulation is really a situation that can show that he is waking up after the operation," Feldman told Channel 2. "This is the first time that we have a positive indication regarding his condition."

However, other neurosurgeons not involved in Sharon's treatment said a full recovery was unlikely after such a massive stroke. Sharon aides said they assume he would not return to work."

I'm worried about the future of this country, about everything in this country," said Rafael Levy, a 42-year-old construction engineer from Tel Aviv.

Sharon underwent seven hours of surgery Thursday at Hadassah Hospital after suffering a brain hemorrhage. He will remain sedated and on a respirator for two to three days to give him time to recover, and then he will be gradually awakened, hospital officials said. His sons, Omri and Gilad, were by his side at the neurological intensive care unit.

Sharon's collapse less than three months before March 28 elections left in limbo his moderate Kadima Party, which had appeared headed for an easy victory.

Palestinians reacted with a mixture of glee at seeing the fall of their longtime enemy and apprehension at the instability that could follow. Some Palestinian leaders worried Sharon's illness could derail their Jan. 25 parliamentary elections. "We are watching with great worry at what might happen if he is harmed," Palestinian leader Mahmoud Abbas said.

Foreign leaders, who embraced Sharon after his unilateral pullout from the Gaza Strip last year, also expressed concern.

US Secretary of State Condoleezza Rice praised Sharon as "a man of enormous courage," and British Foreign Secretary Jack Straw said he was praying for a miraculous recovery. Japanese Prime Minister Junichiro Koizumi postponed a visit to the region, and two U.S. envoys who were to arrive Thursday delayed their trip.

Two prominent rabbis went to Sharon's room on the heavily guarded seventh floor of the hospital and prayed along with his family, one of them, Rabbi Yitzhak Batzri, told Israel Radio. He added that his father, leading Jewish mystic David Batzri, held Sharon's hand to direct a prayer toward him.

"We saw the greatest doctors standing beside him and watching over him all the time and trying to treat him," Yitzhak Batzri said. "He is unconscious as everyone knows and the small happiness that we have is that we saw the family is strong, the family believes, the family is praying and hoping."

Under Israeli law, vice premier Olmert took office as acting prime minister. He held an emergency Cabinet meeting Thursday — sitting beside Sharon's empty seat — and said the government would continue to function.

"This is a difficult situation," Olmert, a former Jerusalem mayor, told the ministers.

He later spoke with Abbas by telephone. The Palestinian leader expressed concern for Sharon and wished him a speedy recovery, Palestinian officials said.

Attorney General Meni Mazuz announced that the Israeli election would be held as planned. Sharon was to face off against the new head of his former Likud Party, Benjamin Netanyahu, and Labor Party leader Amir Peretz.

Sharon had been expected to win in a landslide as head of Kadima, which he formed after bolting Likud late last year. Many Likud lawmakers tried to torpedo the Gaza withdrawal and Sharon formed Kadima to free his hands to make further peace moves with the Palestinians.

His stroke clouded his party's prospects.

"I can't see another person who will emerge who is as strong as Sharon," said political analyst Menachem Hofnung. "The party is in trouble."

Haim Ramon, a Kadima lawmaker, said the party needed to rally around Olmert.

"We have to convince the public that the group that came together with Sharon will fill the political, ideological, societal void, which is needed for the country to go on," he told Channel 2.

A snap poll Thursday showed an Olmert-led Kadima would still win 40 of 120 seats, similar to the results under Sharon. Under former Prime Minister Shimon Peres, the party would get 42 seats, according to the Channel 10-Haaretz poll. The number of people polled and the margin of error were not given

Despite Sharon's age and the minor stroke he suffered two weeks ago, Israelis seemed shocked by the illness of a man viewed as unflappable during his decades in public life, first as a hero in Israel's earliest wars and later as the country's best known political hawk.

Sharon led Israel's fight against the Palestinians during nearly five years of violence and his military background gave him the credibility with the Israeli public to make concessions to the Palestinians.

"He was one of a kind. I don't know any other man like him," said Joseph Lapid, head of the opposition Shinui Party.

Sharon rose to prominence as an army officer, setting up a unit that fought Palestinian infiltrators in the 1950s. He served as a commander of the Gaza region after Israel captured the territory in 1967, before entering politics and forging the Likud Party. Sharon briefly returned to the army to lead the fight against Egypt during the 1973 Mideast war.

As defense minister, Sharon directed Israel's ill-fated invasion of Lebanon in 1982 and was forced to step down by an Israeli commission of inquiry that found him indirectly responsible for a massacre of Palestinians in two refugee camps by Christian Phalangist soldiers.

Sharon re-emerged as prime minister in 2001 soon after the outbreak of new Israeli-Palestinian violence, and two years later he reversed his decades-long support for Jewish settlement and pushed through his Gaza pullout plan.

Despite the pullout, Sharon is widely reviled in the Arab world for his tough actions against Palestinians.

Some Palestinian children handed out sweets in the Gaza Strip at news of Sharon's illness. Other Palestinians worried that it could delay their upcoming elections.

Sharon fell ill Wednesday evening while resting at his ranch in southern Israel ahead of a medical procedure scheduled for Thursday to close a small hole in his heart. Doctors rushed him to Jerusalem, and he suffered the stroke during the hourlong drive.

Doctors said they stopped the bleeding during surgery. His condition may have been complicated by blood thinners he took after his mild stroke Dec. 18