Prime Minister Ariel Sharon could be sedated for up to three days as doctors fight to keep him alive after emergency brain surgery for his massive stroke, a hospital official said Thursday.

Dr. Shlomo Mor-Yosef, director general of Hadassah Hospital, said Sharon would remain in deep sedation and on a respirator for at least two and possibly three days to allow him to "recover from severe trauma." The treatment would decrease pressure in Sharon's skull, and after the sedation period, doctors hope to gradually awaken him, Mor-Yosef said.

Sharon, who underwent seven hours of emergency surgery to stop widespread bleeding in his brain, was in serious but stable condition. The massive stroke made it unlikely that the 77-year-old prime minister would return to power.

Mor-Yosef said doctors had not received a "no resuscitation order" that would prevent them from trying to revive a patient whose heart or breathing has stopped.

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

Israeli TV's Channel 2 station quoted an unidentified senior hospital official as saying Sharon was not in a vegetative state, and Mor-Yosef 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," Mor-Yosef said at a news conference. Other doctors not involved in his treatment said this was a positive sign of independent brain activity.

Mor-Yosef said the surgery was carried out on the right side of Sharon's brain. That could make it less likely that his speech and comprehension would be impaired. The doctor said it was too early to assess whether there would be any paralysis.

A brain scan after surgery showed that the bleeding had been stopped, and he was transferred to the intensive care unit, Mor-Yosef said earlier in the day.

Sharon's sudden illness, at the height of his popularity, stunned Israelis who had relied on the tough ex-general to steer them through turbulent times. Rabbis called on Israelis to flock to synagogues and say special prayers.

The daily newspaper Yediot Ahronot ran a headline that said: "The last battle."

Sharon's sons, Omri and Gilad, were at their father's bedside. Rabbi David Grossman, a family friend, said of them: "You don't see tears. You see hope, quiet and fortitude."

Sharon was put in an ambulance at his ranch Wednesday evening after complaining of feeling ill. The stroke came during the hourlong drive to Hadassah, Dr. Shmuel Shapira told Channel 10 TV.

Doctors at Hadassah put him on a respirator and began emergency surgery about midnight (5 p.m. EST Wednesday). They said they had stopped the bleeding during initial surgery, but Sharon was sent back to the operating room because a brain scan showed he required more treatment.

The surgery apparently had been complicated by an anticoagulant Sharon took following a mild stroke Dec. 18. The medication may also have contributed to Wednesday's stroke. Sharon originally had been scheduled to undergo a procedure Thursday to seal a hole in his heart that contributed to the initial stroke.

Independent experts said that while the medication, an anticoagulant called enoxaparin, did not cause the blood vessel in Sharon's head to burst, the bleeding would probably not have been so severe if he had not been taking it.

Mor-Yosef defended the treatment, saying he was given appropriate doses.

He did not give a prognosis, but neurosurgeons not involved in Sharon's treatment said a full recovery was not likely following such a massive stroke -- especially because of the length of the surgery.

"For them to have to go back in twice, that's not good," said Dr. Emil Popovic, a neurosurgeon at Sir Charles Gairdner Hospital in Perth, Australia. "At 77, not too many people make a good recovery from a brain hemorrhage."

President Bush praised Sharon as "a man of courage and peace," saying he and first lady Laura Bush "share the concerns of the Israeli people ... and we are praying for his recovery."