BEIRUT, Lebanon - Israeli aircraft bombarded guerrilla strongholds in Beirut and southern Lebanon yesterday, doubling the tide of refugees to 400,000 and provoking guerrilla vows to turn northern Israel into a ''fiery hell.''

Undaunted by Israel's four-day-old aerial barrage, Hezbollah guerrillas barraged northern Israel with rockets that came crashing down every 20 minutes for seven hours. One person was wounded and an empty school and other property were damaged.

Three Lebanese civilians were killed and seven were wounded in yesterday's raids, Lebanese security sources said. All told, 28 people have been killed and 105 injured on both sides since the violence began last week.

Israeli jet fighters knocked out a Beirut power relay station, cutting electricity to many parts of the capital and its suburbs. It was the first deliberate attack on an economic target since Israel launched its offensive against the Iranian-backed Hezbollah on Thursday.

The Shiite Muslim Hezbollah opposes Arab-Israeli peacemaking and has been fighting for years to drive Israeli troops from the buffer zone they occupy in southern Lebanon. Daily skirmishes exploded last week into a major Israeli offensive meant to halt a recent wave of Hezbollah attacks on Israel.

About 190,000 panicked Lebanese residents fled the southern port city of Tyre and 41 surrounding villages yesterday after Israel warned it would attack the area at sundown to flush out guerrillas.

Milhem Hussein Milhem, an 80-year-old farmer, escaped with his family of 12.

''My children have not eaten for three days because of the Israeli air raids,'' he said.

Ghonwa Dhahini, 12, and 15 relatives headed north after what she called a ''terrifying night of shelling.''

''I didn't get a single moment of sleep,'' she said.

Some 400,000 refugees - more than half of the population of southern Lebanon and about one-tenth of the country's people - were headed north yesterday for the relative safety of Beirut.

The mass exodus was reminiscent of the last major Israeli strike against Hezbollah, a weeklong offensive in July 1993 that killed 147 Lebanese, wounded about 500, and uprooted half a million people.

With huge numbers of people on the move yesterday, Israeli aircraft struck again.

The southern market town of Nabatiyeh and southeastern villages took the brunt of the raids, which destroyed several houses belonging to Hezbollah commanders.

Israeli aircraft also struck near Tyre, hitting a civil defense ambulance and injuring four paramedics. It was Israel's second helicopter raid on an ambulance in as many days. Saturday's attack killed six civilians, including three children.

The recent violence has engulfed not only the long-tense south but the capital, too, for the first time since Israel invaded Lebanon in 1982 to expel Palestinian guerrillas.

Israel said yesterday's attack on a major Beirut power station was in response to Hezbollah rocket attacks that knocked out electricity in the northern Israeli border town of Kiryat Shemona.

Staccato bursts of anti-aircraft fire from Lebanese and Syrian troops stationed in Lebanon echoed across the capital as the jets swooped down to strike.

Israeli aircraft also attacked Hezbollah's stronghold of southern Beirut. Motorists raced off, tires screeching, and pedestrians dived for cover or cowered at street corners. Eight people were reported wounded.

The Israeli army said the air force attacked ''a target that is used by members of the Hezbollah intelligence and security branches.''

The report could not be verified because Hezbollah gunmen have sealed off guerrilla bases.

Police said Israeli gunboats blocked shipping lanes to Beirut harbor, an apparent attempt to increase pressure on Lebanon's Syrian-backed government to disarm Hezbollah.

Israeli gunboats patrolled off the coast of the northern port of Tripoli, Lebanon's second-largest city, drawing fire from coastal gun batteries manned by Palestinian guerrillas.

In Syrian-controlled eastern Lebanon, Israeli warplanes struck at two transmitters belonging to Hezbollah's Voice of the Oppressed radio station. The station briefly went off the air, then resumed broadcasting on another band.

Ground anti-aircraft fire shot down a pilotless Israeli reconnaissance plane over the Syrian-controlled Bekaa Valley in the east. The drone crashed into a hillside.

With elections just six weeks away, Prime Minister Shimon Peres of Israel has hit hard at Hezbollah in an effort colored partly by a desire to prove he will not let peacemaking compromise Israel's security.

At a weekly Cabinet meeting yesterday, Peres said Israel's military campaign was open-ended, but he added: ''If the Hezbollah ceases its attacks, we will cease ours.''

Hezbollah issued a statement saying it would continue firing rockets on northern Israeli towns and vowed to turn the area ''into a fiery hell.''

Twenty rockets fell on more than a dozen settlements in less than seven hours, and the guerrillas said they had expanded the range of their attacks to Safed, five miles south of the border.

Israel army radio said a public building was severely damaged in a rocket attack on a settlement. Military censors banned publication of the settlement's name.

Channel 2 television in Israel identified the building as a school and broadcast footage of a hole in the roof and damaged classrooms.

One Israeli soldier has been killed and more than 40 Israelis have been wounded.