ASHDOD, Israel - Two Palestinian suicide bombers blew themselves up yesterday at Israel's heavily guarded seaport here, killing 10 other people and wounding at least 20 others in the first successful militant attack on a strategic target in more than three years of fighting.

Israeli authorities said the bombers, high school classmates from the Gaza Strip, may have been trying to reach barrels of bromide and other volatile chemicals stored about 200 yards from where one of the teen-agers detonated his bomb.

"We are very lucky that he didn't get there," said Fire Lt. Israel Topaz, who was among the first emergency workers to reach the scene. "If the bomber had done what we think he had planned, we could be facing mass casualties and all of Ashdod would have had to be evacuated."

Israel responded by canceling a summit tentatively scheduled for tomorrow between Israeli Prime Minister Ariel Sharon and Palestinian Prime Minister Ahmed Qureia. The meeting was to have been an attempt to resurrect a U.S.-backed peace plan that has been stalled for months.

The Islamic fundamentalist group Hamas and the Aqsa Martyrs Brigades claimed responsibility for the attack, another in a recent series of joint operations by organizations that have traditionally been at odds over doctrine and strategy.

A joint statement on fliers circulated in Gaza said the militants "reached the strategic depths in the state of the Zionist entity" and warned that its members could repeat similar missions "anytime we want." They said they were avenging a series of Israeli army attacks in Gaza, including the latest this month that left 14 Palestinians dead.

Ashdod, a city of 206,000, has largely been immune from attacks; the most recent had occurred here two years ago when a Palestinian gunmen opened fire at a wedding reception, wounding a 13-year-old girl.

Zvi Zilker, the city's mayor, stood stunned amid the blinking lights of fire engines and ambulances on a street littered with charred aluminum siding and strewn with branches torn from olive trees. "It's something that happens in Tel Aviv or Jerusalem," he said. "We are used to mourning for others. It's different when it occurs inside our home."

Only a handful of the victims had been identified last night, and no names were released. Officials said nearly all were workers at the port or at a private company across the street that bore the brunt of the second blast.

Investigation continues

Israeli police went on high alert last night in Jerusalem and other cities and said they increased security at Ben Gurion airport, the port at Haifa and at railway stations.

Officials were investigating last night whether the two bombers penetrated a security fence that wraps around the densely populated Gaza Strip, which would mark the first time the barrier has been breached. A Lebanese television station run by the militant group Hezbollah identified the bombers as Nabil Saoud, 17, and Mohammed Salem, 18, 11th-graders from the Gaza Strip's Jabalya refugee camp.

The Gaza fence is held as a model of successful security measures, and is used to help justify a larger barrier being built to separate Israel from the West Bank, from where nearly all of the 112 suicide attacks claiming 450 lives have been launched in the past 42 months.

Summit canceled

Yesterday's blasts occurred shortly after senior Israeli and Palestinian government officials met to set the agenda for the summit between the two prime ministers. Sharon's spokesman, Raanan Gissin, said the attack would accelerate the government's plans to take unilateral steps, such as completing the West Bank barrier and declaring a provisional border.

"On the eve of conducting talks that were supposed to bring them back to the negotiating table, the Palestinian leaders proved they are not willing to take any actions to prevent terrorism," Gissin said. "They bear the same responsibility as those who perpetrated the attacks."

Gissin said the Israeli army was formulating a response. "We will choose the time and place to strike back," he said.

The Palestinian Authority issued a statement condemning the blasts, urged all militant factions to cease further attacks and pleaded with Israeli authorities to agree to a cease-fire "to break the cycle of violence."

Israeli security officials have long worried that Palestinian militant groups, which have typically targeted buses and cafes, would try to commit what they describe as a "mega-terror" attack at an airport or a high-rise tower with hopes of causing large numbers of casualties.