Less than 24 hours after the signing of a major Israeli-Palestinian peace deal, a pair of powerful car bombs exploded in two northern Israeli cities, killing three men who police said apparently were terrorists planning to detonate the bombs in densely populated neighborhoods. One passerby was critically injured.

The seemingly coordinated episodes this afternoon in Tiberias and Haifa -- in which both bombs are believed to have exploded prematurely -- fit a pattern of terror attacks by militant Palestinian groups timed to sabotage Palestinian-Israeli peacemaking whenever it appears to gain momentum. However, there was no immediate claim of responsibility for the incidents. Fearing further attacks, Israeli police set up roadblocks around other towns and cities in the north.

Both Israeli and Palestinian security forces had warned recently that the revival of peacemaking could trigger a resumption of attacks. The militant Palestinian group Hamas, which rejects the peace process and has carried out suicide bomb attacks on Israel in the past, has threatened much the same thing.

Despite what appeared to be an assault on the peace process, stony-faced Israeli officials said tonight they would press ahead with the land-for-peace deal signed early this morning, and they expressed confidence in Palestinian leader Yasser Arafat's determination to fight terror. The Israeli cabinet, which only an hour earlier had voted 21 to 2 to ratify the peace accord, continued its meeting, which by that time had moved on to a discussion of the budget.

Nonetheless, a number of Israelis warned that the resumption of deadly terrorist attacks against the Jewish state, if it continues and claims Jewish lives, could torpedo the plans and timetable for peace laid out in the agreement initialed by Israeli Prime Minister Ehud Barak and Arafat. "If we do not have personal security here in Israel, I believe the peace process is in danger of collapsing," said chief Israeli negotiator Gilad Sher, speaking on CNN.

Arafat telephoned Barak and condemned the attack, and other Palestinian leaders stressed their determination to fight terror and press ahead with peace. "The enemies of peace are attacking those who seek peace, particularly when we take a step forward toward achieving peace," said Nabil Shaath, a top Palestinian negotiator. "We condemn these terrorist acts and condemn everybody who stands behind them."

The bombs exploded about 20 minutes apart, critically injuring an Israeli woman pedestrian in Tiberias, a holiday resort on the western edge of the Sea of Galilee. The bomb exploded around 5:10 p.m. with a deafening roar in an Audi 10 yards from a gas station and less than a mile from the center of town. The driver and his passenger were blown from the mangled car and killed instantly, and the pedestrian suffered massive head and facial injuries. Three others were treated for minor injuries.

Sixty miles to the west, in Haifa, a sprawling Mediterranean port city, a bomb exploded at 5:30 p.m. in a Fiat parked in a lot within blocks of the central bus station, killing the driver. The blast in Haifa, which has a large Arab minority, occurred in a predominantly Arab section of town, possibly as the bomber was preparing the explosives, police said.

Last fall, six days after the signing of a previous peace deal at Maryland's Wye River Plantation, a Palestinian militant drove a car packed with explosives at two buses filled with Israeli school children in the Gaza Strip. The car was blocked from reaching the buses by an Israeli military jeep escort, whose driver was killed in the blast.

That attack prompted Prime Minister Binyamin Netanyahu to put the Wye River deal briefly on hold, stirred doubts about the chances for peace among some moderate Israelis and inflamed hard-liners, who said it proved that dealing with the Palestinians was impossible.

Today, too, even though the blast killed no Jews, there were stirrings of anger in Israeli public opinion. "I'm afraid that with the Palestinians we can't make peace," said Yaacov Gabay, 43, a fisherman who was driving 10 yards behind the car that exploded in Tiberias. "Yesterday, we had a nice signing ceremony; now today they blew up a car in our town. The government should stop all talks now. This [process] is one-sided. We give, but we get no security in our homes."

Gabay and other witnesses said the Audi erupted with a concussive blast that blew away the rear three-quarters of the vehicle.

Since the signing of the Wye accord last October, Arafat's autonomous Palestinian Authority, which controls portions of the West Bank and Gaza, has cracked down on Hamas, Islamic Jihad and other militant groups, rounding up scores of activists. The founder and spiritual leader of Hamas, Sheik Ahmed Yassin, was placed under house arrest for weeks after the attempted attack on the school buses last fall.

Hamas has complained bitterly at this treatment, which it attributes to Israeli and U.S. pressure on Arafat. Although Israeli hawks insist Arafat has not done enough to uproot the groups behind terrorist attacks, other analysts speculated that Hamas had been nearly crippled by Arafat's moves against it. Nonetheless, the group -- which Israel contends is backed by Iran -- has vowed to continue prosecuting what it calls its jihad, or holy war, against the Jewish state, whose existence the group opposes.

"People will soon be happy to hear the good news about our jihad operations in the near future," said a statement signed by Hamas's armed wing, the Izz-al Deen al-Qassam Brigades, and faxed to news agencies in Jerusalem in July. Although the authenticity of the statement could not be confirmed, Israeli analysts called it all too plausible.

Most Palestinians do not support terror attacks against Israel, which they regard as only impeding progress toward the tangible benefits of peace, including the release of Palestinians imprisoned by Israel and the easing of travel restrictions between the West Bank and Gaza. In the past, terror attacks have also prompted Israel to bar Palestinian workers from entering the country, costing tens of thousands of struggling Palestinian families dearly.

Hockstader reported from Jerusalem, O'Connor from Tiberias.