JERUSALEM (AP) - Prime Minister Ariel Sharon suffered a massive, life-threatening stroke yesterday and underwent lengthy surgery to drain blood from his brain after falling ill at his ranch. Powers were transferred to his deputy, Ehud Olmert.

Israeli TV stations reported that Sharon was alive after an operation that lasted more than six hours.

Doctors placed Sharon on a respirator and were trying to save his life only hours before the hard-charging, overweight, 77-year-old Israeli leader had been scheduled to undergo a procedure to seal a hole in his heart that contributed to a mild stroke on Dec. 18.

Israel Radio quoted an unidentified Israeli health official as saying that Sharon's prospects of a full recovery were slim. As his doctors operated on Sharon's brain through the night, Israeli media reported the blood draining phase was completed, and surgeons were working to cauterize the bleeding vessels.

Sharon's cerebral hemorrhage, or bleeding stroke, came at a time of upheaval among Palestinian factions in Gaza and in the midst of both Israeli and Palestinian election campaigns. Sharon's absence would slow momentum toward peacemaking with the Palestinians and leave a major vacuum at the head of his new Kadima party, which was expected to head a government after the March 28 vote.

In a written statement, 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."

Israeli Chief Rabbi Yona Metzger called on Israelis to read Psalms and pray for Sharon. "We are very, very worried," he said, and prayed for "mercy from Heaven."

Pan-Arab satellite television broadcasters beamed out largely straightforward, nonstop live coverage from outside the hospital where Sharon - a particularly despised figure among many Arabs - struggled for his life.

A radical Palestinian leader in Damascus, the Syrian capital, called the stroke a gift from God.

"We say it frankly that God is great and is able to exact revenge on this butcher. - We thank God for this gift he presented to us on this new year," Ahmed Jibril, leader of the Syrian-backed faction Popular Front for the Liberation of Palestine-General Command, a small radical group, told The Associated Press.

Speaking to reporters outside the hospital, Sharon aide Raanan Gissin warned Israel's enemies: "To anyone who entertains any notion to try and exploit this situation - the security forces and IDF (Israeli military) are ready for any kind of challenge," he said.

But a Palestinian commentator on the Saudi-owned Al-Arabiya network offered Sharon unexpected praise as "the first Israeli leader who stopped claiming Israel had a right to all of the Palestinians' land," a reference to Israeli's recent withdrawal from the Gaza Strip.

"A live Sharon is better for the Palestinians now, despite all the crimes he has committed against us," said Ghazi al-Saadi.

Sharon's personal physician said early Thursday that he expects Sharon to emerge from surgery "safely."

"The prime minister is currently in surgery, it is proceeding properly," said Dr. Shlomo Segev. "We need to wait patiently. I expect him to emerge from it safely."

But Channel 2 TV said the prime minister was suffering from paralysis in his lower body, and medical experts who have not examined Sharon said chances are slim for a complete recovery.

"It's among the most dangerous of all types of strokes," with half of victims dying within a month, said Dr. Robert A. Felberg, a neurologist at Ochsner Clinic in New Orleans.

"The fact that he's on a respirator means it's extremely serious," said Dr. Philip Steig, chair of neurosurgery at Weill-Cornell Medical Center in New York.

Larry Goldstein, director of Duke University's stroke program, said much depends on the extent, location and duration of the bleeding.

"Bleeding in some areas of the brain, if it's caught early enough, you can actually have not a bad outcome," he said.

Sharon was put in an ambulance at his ranch in the Negev Desert after complaining about feeling unwell. The stroke happened during the hourlong drive to Hadassah Hospital in Jerusalem, Dr. Shmuel Shapira of the hospital told Channel 10 TV.

Dr. Shlomo Mor-Yosef, director of Hadassah Hospital, said Sharon suffered "a significant stroke," adding that he was "under anesthetic and receiving breathing assistance."

A few minutes later, Mor-Yosef emerged to say that initial tests showed Sharon had suffered a cerebral hemorrhage, or bleeding in his brain.

Mor-Yosef said Sharon had "massive bleeding and was being transferred to an operating theater."