Palestine Liberation Organization Chairman Yasser Arafat arrived here by boat today from the Lebanese capital of Beirut, claiming victory for the guerrillas over Israel and promising to continue the Palestinian struggle for a homeland "by all means."

He was greeted warmly at dockside by Greek Prime Minister Andreas Papandreou and other top government officials as a small crowd of mostly Greek Socialist Party members and Palestinians stood by chanting slogans supporting the Palestinian cause.

At a later press conference, the Greek leader called Arafat's arrival in Athens an "historic moment" and assured him of Greece's full support in the Palestinians' struggle for "full autonomy, their own homeland and their own state."

Arafat, looking relaxed, smiled after his long ordeal in Beirut and denied that his guerrilla forces, the last of whom where evacuated from Beirut today, had been defeated in the Israeli 10-week siege of Beirut.

"It is my honor and my pride that I prevented these barbarian savage Israeli troops from invading Beirut," he said. "I am with the people, and no people can be defeated."

Arafat arrived in Greece just six hours before French President Francois Mitterrand, who is here for a two-day state visit. The Greek luxury liner Atlantis carrying Arafat and a small group of his top lieutenants and security men arrived about noon and docked at a marina for large yachts at Flisvos, six miles southeast of Athens.

Papandreou's personal welcome at dockside came after earlier indications that the Papandreou government intended to give Arafat's visit little publicity. The two men then held a joint press conference at the Apollon Hotel in the suburb of Kavouri, 15 miles southeast of Athens, where the Palestinian chief and his party are staying.

Papandreou predicted that Western European nations would continue to give the PLO their "active support" and said it was time that "a final solution be found to this Palestinian problem."

Greece is the only member of the European Community to grant full diplomatic recognition to the PLO, and Papandreou last December received Arafat in the equivalent of an official state visit here.

Arafat, for his part, vowed to continue the Palestinian struggle against Israel for an independent state "by all means," indicating he meant both military and political ones.

"We are under occupation. They [the Israelis] are occupying our land. We have the right to use all methods and means to continue our struggle," he said. "People have a right to resist against occupation."

But he was evasive when asked how the PLO, with its guerrilla forces now spread among eight Arab nations, could continue armed struggle alone.

He was also vague about political options available to the PLO. In answer to one question, he said that the PLO would declare a government in exile "as soon as we find it is suitable to declare it."

Arafat said that the top PLO leadership, most of which is in Syria and Tunisia, planned to hold a number of high-level meetings to discuss this and other plans shortly.

The Palestinian leader and his lieutenants are expected to leave here Thursday or early Friday for Tunis before traveling on to Morocco next Monday for a scheduled summit of Arab leaders.

Arafat did not confirm, however, that he definitely planned to attend the summit and said this would be discussed by the PLO leadership in the next few days.

Asked about the possibility of a meeting with Mitterrand here, Papandreou answered for Arafat, saying "the president of France wants to see the head of the PLO in France, not in Greece." There was no confirmation of this reported French willingness to host Arafat in Paris, however.

Arafat also said a U.S. guarantee for the protection of more than 500,000 Palestinian civilians left behind in Lebanon after the guerrilla exodus was "fundamental" to the PLO agreement to leave Beirut.

"We couldn't have had an agreement without it," he said.