Palestine Liberation Organization Chairman Yasser Arafat gave up his base in Lebanon and sailed to Greece today, but he vowed in an emotional farewell "to continue the struggle so we can win the war" against Israel for a Palestinian state.

Forced out of Beirut by the 10-week Israeli siege of the Lebanese capital, the guerrilla leader decried the lack of support from Arab governments and warned that they "will soon be shaken by Beirut's erupting volcano."

The evacuation was nearing completion today with the departure of Arafat and the first Syrian troops to leave the city. The 1,500 soldiers, who came in 1976 as part of an Arab Deterrent Force to keep peace after Lebanon's civil war, went in about 250 trucks and buses and took 10 Soviet-built tanks, several armored vehicles and a number of artillery pieces.

Syrian radio said they withdrew only to the Bekaa Valley in eastern Lebanon rather than to Syria. Syrian and Israeli forces clashed in the area before the evacuation was arranged, and there are fears that the strategic valley could be a new theater of warfare after the Beirut evacuation is completed.

The Lebanese rightist radio station Voice of Lebanon reported that a Syrian Mig23 jet fighter was shot down early Tuesday in a dogfight with Israeli warplanes in the Lebanese mountains east of Beirut, United Press International reported. There was no immediate confirmation.

More than 9,000 Palestinian fighters and members of the Syrian-controlled Palestine Liberation Army have now left Beirut, according to unofficial counts. Although the exact numbers have been questioned by the Israelis, only a small number of Palestinian and Syrian fighters are believed still to be in the city, and the evacuation arranged by U.S. special envoy Philip C. Habib is expected to be finished within several days.

Arafat's departure from Beirut's crumbling port, shattered by seven years of bombardment in Lebanon's civil unrest and the recent Israeli assault, was a scene of chaos as hundreds of his supporters surrounded him in a human wave seeking to get a last look at their leader before he boarded the Greek passenger ship Atlantis.

A Greek government spokesman said today that Arafat is expected to meet briefly with Prime Minister Andreas Papandreou after arriving in Greece and to leave "again the same day or early Thursday." Arafat is expected eventually to establish a new base in Tunisia. He was accompanied by 62 PLO officials, bodyguards and family members.

By choosing to go first to Greece for an official visit, he appeared to be snubbing his Arab allies for their failure to support the PLO against the Israeli invasion.

However, he was also sending a message to Israel that the PLO has friends in the West despite a call just two days ago by Israeli Foreign Minister Yitzhak Shamir for Western nations to boycott the PLO.

Arafat's visit in Athens will coincide with an official visit there by French President Francois Mitterrand, but the two leaders are not expected to meet, according to a Greek government official.

A spokesman for Mitterrand in Paris confirmed that the French president does not plan to meet Arafat in Greece, Reuter reported.

For days, Arafat's departure plans had been shrouded in mystery although he has held a series of good-bye meetings with people here. He started today by racing at breakneck speed through Beirut traffic to pay farewell calls on Moslem leaders and then entered the port area to be greeted by bursts of gunfire.

Plans for an honor guard of his forces to present their flags were abandoned as the troops broke ranks and melted into the maelstrom after Arafat -- dressed in his traditional military fatigues, checkered Arab headdress and beaded necklace in the Palestinian colors -- stepped out of the bulletproof limousine of Prime Minister Shafiq Wazzan.

Despite the emotional scenes and the danger of physical injury as his shouting backers swarmed around him, Arafat was calm and silent.

The roof of the vehicle almost collapsed from the weight of television cameramen and supporters trying to follow him past Lebanese soldiers and U.S. Marines into the port.

The ragged procession, guided by hardened veterans of the French Foreign Legion, took almost 10 minutes to negotiate the last 25 yards to the gates of the port.

Onlookers last saw Arafat as he passed through the ranks of the Marines to proceed shortly before 11 a.m. to the Atlantis, a gleaming white, single-stacked cruise ship.

On the ship Arafat said his final farewells to leading Lebanese Moslem politicians including Wazzan and former prime minister Saeb Salam, and the ambassadors of France, Greece and North Korea.

Shortly before noon the Atlantis gave a long horn blast and set sail, escorted by U.S. and French warships, as Moslem militia units unleashed salvos of artillery and antiaircraft fire.

Despite the chaotic departure, exceptional security precautions had been taken for fear of a possible attempt on Arafat's life. Outside the port entrance, a French armored car and three truckloads of French troops from the multinational peace-keeping force supervising the Palestinian withdrawal were in charge.

About three dozen Lebanese troops formed a line at the entrance and behind them were a similar number of Marines, many of them in sandbagged positions atop crumbling buildings on the lookout for snipers. The French troops sifted through the rubble outside for possible explosives.

Many of Arafat's bodyguards drove through the gates earlier wrapped almost entirely in their headdresses to prevent identification.

There were also numerous civilian-clothed guards, some with shotguns. One guard wore a T-shirt emblazoned "U.S. Marines, American Embassy, Beirut." He had divided loyalties in his firepower, however, carrying a Russian-designed AK47 rifle and wearing a U.S.-made .45-caliber pistol.

Arafat's departure came 86 days after the Israeli invasion of Lebanon, which led to the U.S.-negotiated withdrawal of the PLO from Beirut to prevent an Israeli assault.

In farewell remarks, Arafat praised the Lebanese people for their hospitality and said, "Part of my heart stays here."

"This is one station. I'm going to another station," he said. "The long march continues."

Criticizing the lack of Arab world support, he said, "Snows of Mount Hermon [in Lebanon] were warmer than the hearts of some of the Arab regimes."

Salah Khalaf, one of the key Arafat deputies still in Beirut, took a harder line at a press conference shortly after the chairman's departure. The PLO would not abandon its military options despite being dispersed to eight Arab nations, Khalaf, also known as Abu Iyad, said.

"There is no such thing as a political PLO," he said. "If before the war we were convinced of the importance of the armed struggle, we are convinced 10 times more now."

He discounted the difficulties of carrying on such a fight from widely scattered countries, saying, "We have experienced previous exoduses. This is our fourth exodus," a reference to being driven out of Palestine in 1948, the West Bank and Gaza in 1967 and Jordan in 1970.

"We were fighting alone, and we owe no debts to anyone," he added. "Every Arab state owes debts which we collect at the appropriate time and place."

Khalaf, who sometimes takes a harder line than Arafat, said the PLO was opposed to next week's planned Arab summit in Morocco, maintaining that one should have been held while the war was still going on.

He said the organization would attend but did not want Egypt or Lebanon's President-elect Bashir Gemayel, who has been backed by the Israelis, to attend. He also said that a Saudi peace plan, which gives implicit recognition to Israel, should not be on the agenda.