BEIRUT, Lebanon — The Lebanese capital was under siege yesterday as Israel imposed an air and sea blockade in response to the kidnapping of two of its soldiers by Hezbollah.

Israel’s action cast a pall over Beirut, which had finally begun to stand on its own feet again after decades of war and depredation.

Residents awoke to the news that Rafik Hariri International Airport had been closed after the runway was bombed and that Israeli warships had blocked all Lebanese ports.

People began fleeing in case of further attacks. With the sea outlets blocked, the main traffic was concentrated near the gas pumps. Huge jams built up as motorists filled their tanks.

“Why are the Israelis attacking us?” cried Hassan Jammal in the Muslim neighborhood of Hamra as he filled up. “Why are they cutting off our country? Is this a proper response to one kidnapping — to cripple a whole nation?”

The general mood was at first somber and resigned. But it grew to panic as the day progressed. Roads from the city into the mountains to the north and east were crowded with cars.

But in the Hezbollah stronghold of Haret Hreik, a southern suburb, the mood was defiant despite a general alert from Israel saying that all residents of the neighborhood should leave immediately before air attacks were launched.

Overnight, Israel had bombed the Hezbollah security block and an office of al-Manar Television, the militant Shiite group’s broadcasting station, although it was still on the air last night.

Israel also attacked Hezbollah strongholds in the Bekaa Valley and launched air raids against a Shiite prayer house and another Manar transmission station. More than 52 civilians have been killed so far.

“We will not leave,” a Hezbollah supporter, Ibrahim Mansour, said, echoing comments from official spokesmen. “We will retaliate with force and damage the Israelis where it hurts them most and attack Haifa and all the towns of northern Israel if they attack Beirut and our homes.”

But after the Israeli warning of an attack, civilians were fleeing in cars, vans, and buses. The roads out of the suburb were crammed with vehicles.

The owner of a DVD store, who gave his name only as Ali, said Hezbollah would retaliate. “We have not stopped being at war with Israel,” he said. “We forced them to leave the country once and we will fight them now.”

Throughout the day, Hezbollah sent Katyusha rockets towards border towns in Israel from the south of Lebanon and said they would repel any invasion.

“We are becoming more afraid,” a cafe owner said.”We don’t know who or what is going to be hit tonight. None of us expected Hezbollah to act in this way. But the Israeli response will ruin our economy and the summer tourist season. “

The single customer in the cafe said: “Hezbollah knew there would be massive retaliation for this. Why did they do this now? They have hurt themselves in the eyes of the Lebanese. We just want peace and to have normal lives.”