Israel staged ground, air and sea attacks on southern Lebanon today, continuing for the 11th straight day its assault on Palestinian facilities there in defiance of a U.S. effort to arrange a cease-fire in the worst surge of fighting here in three days.

It was the first time since May 28 that Israeli ground forces attacked sites in Lebanon, although air and naval forces have been bombarding the country almost daily. The general assumption here is that larger ground attacks will follow soon, as Israel seeks to carry out its public pledge to escalate its war on the Palestinian guerrillas who use southern Lebanon as a base to raid and shell northern Israel.

The Palestine Liberation Organization leader, Yasser Arafat, accused Israel today of waging an "unhumanitarian war of annihilation" against the Palestinians and carrying out "barbaric air raids" against civilians. He accused President Reagan of giving Israeli Prime Minister Menachem Begin a "green light" to wage war against the Palestinians in Lebanon.

The first Israeli attack today came shortly after midnight when helicopter-borne commandos stormed a guerrilla stronghold on the Zahrani estuary, about 27 miles south of Beirut, under the cover of fire from nearby Israeli gunboats.

Local sources in Sidon, just north of the Zahrani estuary, said the Israeli commandos blew up ammunition and weapons depots at Fannar and Mseileh, 2 1/2 miles inland, and attacked three other strongholds belonging to Arafat's Fatah organization, the largest within the PLO, in the same area.

The Palestinian news agency, WAFA, said the assault on Mseileh, where the leftist Lebanese Arab Army has a base, was beaten off. It also said an Israeli attempt to land commandos by sea was repulsed, with one gunboat set ablaze. But the Israeli military command denied there was any such effort to put commandos ashore from boats.

The Israeli command said an Israeli major was killed and seven soldiers were wounded in the half-hour attack and "a number of terrorists" were killed. The number of Israeli casualties was regarded here as fairly high for a small Israeli operation, appearing to corroborate the Palestinians' claim that it had run into stiff resistance.

The Sidon sources said one guerrilla was killed and three were wounded from the Lebanese Arab Army, which supports the Palestinians, and a dozen others from Fatah were wounded in the night fighting.

A prime target of the current Israeli campaign against the Palestinian guerrillas is believed to be the heavily fortified 12th century Beaufort Castle, which sits atop a bluff overlooking the Litani River in southern Lebanon and is used as a main launching point for guerrilla rockets that have been hitting villages all across northern Israel.

Israeli warplanes bombed the castle today and also hit guerrilla strongpoints around nearby Nabatiyeh. They also returned to the Zahrani estuary to bomb Palestinian sites there. An oil refinery, which provides a third of Lebanon's gasoline, is located at Zahrani and has been put out of operation by the recent bombing.

Reporters visiting the area today saw considerable damage. Israeli bombs have destroyed not only a key bridge carrying a major north-south highway across the Zahrani but also several buildings and installations around the refinery. Nearly a dozen oil-delivery trucks have been gutted.

All of Lebanon from Beirut south is in the grips of an acute gasoline shortage and there are long lines at stations that are still open.

Despite the Israeli destruction of several key bridges and attempts to cut the road by bombings, the main coastal highway remains open all the way from Beirut to Tyre. The Lebanese and Palestinians have quickly built bypasses and repaired the roadway.

There was little sign of Palestinian guerrillas anywhere along the highway today. Guerrillas were halting traffic near the Litani River, however, because long-range Israeli artillery was bombarding a badly damaged bridge across the river as well as a makeshift bypass.

Arafat, speaking at a news conference for the first time since the devastating Israeli bombing of downtown Beirut on Friday, in which at least 300 people were killed and 700 wounded, Arafat charged that Begin was seeking a "final solution" to the Palestinian problem in the same manner as Adolf Hitler had tried to do with the Jews during World War II.

The Palestinian leader justified his guerrillas' shelling of Israeli villages, which today killed a fifth civilian, and said he had a "mutual responsibility" to defend his people.

"We are human beings, too," he said. "They have to remember the blood of our women and children is precious, too."

Arafat attacked Reagan for supporting Israel and said, "We are facing this decision, an American decision, [carried out] through this Israeli military junta."

Asked about special U.S. envoy Philip C. Habib's efforts to negotiate a cease-fire, Arafat said only that "we cannot say a lot now but discussion is going on." He reiterated the PLO's longstanding demand for a "just settlement" including a Palestinian state and the right of Palestinians to return to a homeland.

Habib, who had two meetings with Begin yesterday, met today with opposition Labor Party leader Shimon Peres before leaving Israel for Beirut.