GAZA  Waves of Israeli airstrikes destroyed Hamas security facilities in Gaza on Saturday in a crushing response to the group’s rocket fire, killing more than 225  the highest one-day toll in the Israeli-Palestinian conflict in decades.

Israeli military officials said the airstrikes, which went on into the night, were the start of what could be days or even months of an effort to force Hamas to end its rocket barrages into southern Israel. The operation could include ground forces, a senior Israeli security official said.

Palestinian officials said that most of the dead were security officers for Hamas, including two senior commanders, and that at least 600 people had been wounded in the attacks.

Image Palestinian protesters threw stones at Israeli soldiers in clashes near Jerusalem on Saturday. Credit... Ahmad Gharabli/Agence France-Presse — Getty Images

After the initial airstrikes, dozens of rockets were fired into southern Israel, where an emergency was declared. Thousands of Israelis hurried into bomb shelters amid the hail of rockets, including some longer-range models that reached farther north than ever before. One man was killed in the town of Netivot, the first death from rocket fire since it intensified a week ago, and four were wounded.

A number of governments and international officials, including leaders of Russia, Egypt, the European Union and the United Nations, condemned Israel’s use of force and also called on Hamas to end the rocket fire. But in strong terms, the Bush administration blamed Hamas for the violence and demanded that it stop firing rockets.

A military operation had been forecast and demanded by Israeli officials for weeks, ever since a rocky cease-fire between Israel and Hamas fully collapsed a week ago, leading again to rocket attacks in large numbers against Israel and isolated Israeli operations here.

Still, there was a shocking quality to Saturday’s attacks, which began in broad daylight as police cadets were graduating, women were shopping at the outdoor market, and children were emerging from school.

Image An injured Palestinian was helped from the rubble after an Israeli airstrike struck Rafah in the Gaza Strip on Saturday. Credit... Hatem Omar/Associated Press

The center of Gaza City was a scene of chaotic horror, with rubble everywhere, sirens wailing, and women shrieking as dozens of mutilated bodies were laid out on the pavement and in the lobby of Shifa Hospital so that family members could identify them. The dead included civilians, including several construction workers and at least two children in school uniforms.

By afternoon, shops were shuttered, funerals began and mourning tents were visible on nearly every major street of this densely populated city.

The leader of the Hamas government in Gaza, Ismail Haniya, said in a statement that “Palestine has never witnessed an uglier massacre.” Later, in a televised speech, he vowed to fight Israel. “We say in all confidence that even if we are hung on the gallows or they make our blood flow in the streets or they tear our bodies apart, we will bow only before God and we will not abandon Palestine,” he said.

In Damascus, Syria, Hamas’s supreme leader, Khaled Meshal, said in an interview with Al Jazeera television that he was calling for a new Palestinian intifada against Israel, including the resumption of suicide attacks within Israel for the first time since 2005. Hamas, he said, had accepted “all the peaceful options, but without results.”

Image Israelis in a bomb shelter in the town of Netivot watched Ehud Barak, the Israeli defense minister, on television. Dozens of rockets struck southern Israel after the airstrikes in Gaza, sending residents underground. Credit... Rina Castelnuovo for The New York Times

Ehud Barak, the Israeli defense minister and chairman of the Labor Party, said the military operation in Gaza would expand and deepen as necessary, adding, “There is a time for calm and a time for fighting, and this is the time for fighting.”

“We wanted to attack military targets while the terrorists were inside the facilities and before Hamas was able to get its rockets out that were stored in some of the targets,” said a top Israeli security official, briefing a group of reporters by telephone on condition of anonymity.

“Right now, we have to hit Hamas hard to stop the launching,” he added. “I don’t see any other way for Hamas to change its behavior. Hamas is not just a terrorist organization. It actually rules Gaza and is well supported by Iran with some of its leadership in Syria.”

Hamas had in recent weeks let it be known that it doubted Israel would engage in a major military undertaking because of its coming elections. But in some ways the elections have made it impossible for officials like Mr. Barak not to react, because the public has grown anxious and angry over the rocket fire, which while causing no recent deaths and few injuries is deeply disturbing for those living near Gaza.

Image Plumes of dark smoke rose from Gaza City during the Israeli airstrike. Credit... Edi Israel/European Pressphoto Agency

Israeli officials said that anyone linked to the Hamas security structure or government was fair game because Hamas was a terrorist group that sought Israel’s destruction. But with work here increasingly scarce because of an international embargo on Hamas, young men are tempted by the steady work of the police force without necessarily fully accepting the Hamas ideology. One of the biggest tolls on Saturday was at a police cadet graduation ceremony in which 15 people were killed.

Spokesmen for Hamas officials, who have mostly gone underground, called on militants to seek revenge and fight to the last drop of blood. Several compared what was happening to the 2006 war between Israel and the Lebanese militia Hezbollah, when Israel reacted to the capture and killing of soldiers along its northern border with air raids, followed by a ground attack. Hezbollah is widely viewed as having withstood those assaults and emerged much stronger politically.

The Arab League initially called an emergency meeting for Sunday in Cairo with all the foreign ministers from the member states, but later postponed it to Wednesday to give ministers time to respond.

Governments that dislike Hamas, like Egypt’s, Jordan’s and the Palestinian Authority in the West Bank, are in a delicate position. They blame Hamas for having taken over Gaza by force 18 months ago in the aftermath of its election victory in the Palestinian Parliament, and they oppose its rocket fire on Israeli towns and communities.

Image Palestinians evacuated a wounded man after an Israeli air strike on Hamas compounds in Gaza on Saturday. Credit... Suhaib Salem/Reuters

But the sight of scores of Palestinians killed by Israeli warplanes outraged their citizens, and anti-Israel demonstrations broke out across the region.

President Mahmoud Abbas of the Palestinian Authority angrily condemned the Israeli airstrikes. Egypt, worried about possible efforts by Palestinians to enter the country, has set up machine guns along the Gaza border. But on Saturday it temporarily opened the Rafah border crossing in order to allow the wounded to be brought to Egyptian hospitals.

In the West Bank and in some Arab parts of Jerusalem and Israel, Palestinians threw stones, causing some injuries.

Hamas is officially committed to Israel’s destruction, and after it took over Gaza in 2007, it said it would not recognize Israel, honor previous Palestinian Authority commitments to it or end its violence against Israelis.