JERUSALEM – Israeli Prime Minister Ariel Sharon remained in critical condition Saturday, but a new round of tests revealed a slight improvement in the physical state of his brain.

Despite some positive signs, including evidence suggesting that the side of his brain controlling speech remains unharmed, doctors cautioned that it was too soon to tell whether Sharon would survive the massive stroke and extensive hemorrhaging he has endured in recent days.

“We as people are optimists,” said Shlomo Mor-Yosef, director of the Hadassah-Ein Kerem Hospital, where Sharon is being treated. “But I can’t say that he is out of danger. His condition is still serious. But the scan shows slight improvement.”

Sharon, 77 and vastly overweight, suffered a stroke Wednesday night caused by a blood clot that went to his brain. Doctors have performed three rounds of surgery struggling to control the resulting hemorrhaging, likely caused in part by blood-thinning medication Sharon was taking for a stroke he suffered last month.

The report by Mor-Yosef on Saturday evening was the second consecutive assessment of the prime minister’s condition that announced no new bleeding and a reduction in dangerous swelling that could cause permanent brain damage.

But whether Sharon, who has dominated Israeli’s politics since becoming prime minister nearly five years ago, will recover and do so with his faculties intact remains uncertain.

“The team at Hadassah Hospital, along with the prime minister and the Sharon family, are fighting to save the prime minister’s life,” Mor-Yosef said.

Sharon’s doctors were to meet this morning to decide when to begin rousing him from a coma, medically induced to give his brain a chance to recover from the trauma of the stroke and repeated surgeries.

Only when he is conscious, Mor-Yosef said, will doctors be able to evaluate Sharon’s brain function and any possible damage he has sustained.

Sharon underwent a scheduled brain scan Saturday morning to check for bleeding and to measure pressure inside his skull. A day earlier, a CT scan – a special multiple X-ray screening process that allows viewing of interior body parts – revealed fresh hemorrhaging and a spike in pressure. Sharon was rushed into five hours of emergency surgery.

The operation, in which a catheter was inserted to drain fluid from his skull, stanched the bleeding and reduced swelling. Mor-Yosef said the swelling declined further Saturday and that the prime minister’s vital signs, including blood pressure and urine production, were within “normal ranges.”

The tests also revealed that the left side of Sharon’s brain appeared to be undamaged, a potentially auspicious sign for his recovery.

Sharon’s hemorrhaging occurred on the right side of his brain, meaning he will likely suffer at least some paralysis on the left side of his body if he survives.

But doctors had also feared that the swelling caused by the bleeding may have squeezed the left side of the brain against the skull, causing damage to areas that control speech, faculties of analysis, and fine motor skills such as writing in a right-handed person. Sharon is right handed, according to one of the doctors treating him.

“The only thing we can say is that the left side of the prime minister’s brain remains intact,” Mor-Yosef said. “We will only know what this means when they wake the prime minister up gradually.”

The prime minister was seeking a third term in national elections scheduled for March 28 when he was rushed to the hospital here complaining of chest pains. Sharon, a hawkish former general, is viewed by many Palestinians and much of the Arab world as a villain for his harsh tactics during war and uprising in territory Israel occupied in the 1967. But in recent years Sharon pushed a program of unilateral withdrawals from some of that land, envisioned by Palestinians as their future state, in an attempt to establish what he said would be more defensible borders and move toward settling the conflict on his terms.

Amid the violence of the most recent Palestinian uprising, which began in September 2000, the strategy found broad appeal among centrist Israelis, who had been rallying behind his newly formed Kadima party.

His stroke has caused upheaval in Israel’s political system, and his grave but stable condition has frozen many of the decisions that will determine who might replace him should he be unable to return to office. Most physicians and political figures here believe that will be the case.