It began 17 years ago with 200 volunteers, a handful of weapons, and a mission -- to "liberate Palestine" from its "Zionist occupiers" and return it to those who had lived there before the advent of Israel. It called itself the military wing of "Fatah" and at first its attacks seemed so amateurish and self-destructive that some Arabs accused its leaders of being CIA agents.

But the Fatah guerrillas, and the Palestine Liberation Organization that they came to dominate, survived not only their shaky beginnings but numerous internal splits, wars and crackdowns by both Israel and supposedly friendly Arab governments.

Under the leadership of Yasser Arafat, the PLO burgeoned into a quasi-state with an annual budget believed to exceed a half billion dollars, with schools, factories, hospitals, utilities, social welfare agencies and prisons. It eventually claimed 15,000 fighters and an impressive arsenal of heavy artillery, multiple rocket launchers, antiaircraft guns and missiles and Soviet-made tanks of World War II vintage.

Today, after a crushing military defeat by Israel, the PLO faces its greatest test. With the prospect of a humiliating withdrawal from the country that served as its base for 12 years, and with its forces and leaders about to be scattered to eight Arab countries, the PLO stands on the brink of either disintegration or transformation.

At stake are the two central elements that have contributed to the PLO's influence -- its independence and its command over the loyalties of the world's 4 million Palestinians. The Arab states willing to take in the guerrillas are certain to maintain tighter control over them than did the fractured Lebanese government. Gone will be the days when the PLO made its own laws and enforced them over a large swath of Lebanese territory.

The PLO also is likely to lose control over Lebanon's Palestinian camps, whose refugee populations have provided a vital source of support as well as a raison d'etre for the PLO's large, state-like apparatus. While the camp populations make up a minority of the Palestinians in exile, their refusal to be assimilated into other Arab cultures, or Arab unwillingness to accept them, has helped maintain a Palestinian identity and served as a constant reminder of the PLO cause.

No matter what happens next, PLO leaders and many other Palestinians insist, the PLO will survive in some form because, more than just a political or military organization, it is the embodiment of the national aspirations of the Palestinian people.

"There will always be a PLO irrespective of what happens to Arafat," said one prominent Palestinian in West Beirut. "The PLO came out of the Palestinian personality, and the elements that gave birth to the PLO are still there."

It is unclear how the PLO component groups will be dispersed in the upcoming evacuation and whether the PLO can continue to operate as an umbrella organization. But one likely result, PLO leaders warn, is that they will be in even less of a position to control the activities of splinter groups resorting to international terrorism.

"If the resistance is destroyed in Lebanon, Palestinians are going to have enormous impetus to do horrible things" not only against Israeli and Western targets but against the Arab states deemed to have let the Palestinians down, said one PLO official. "The effect will be even greater than Black September. It will be totally destructive. It will be nihilistic. And it certainly won't do anybody any good."

It remains unclear to what extent, and in what manner, its Arab financial backers will continue to support the PLO. The organization is financed largely by Saudi Arabia and other oil-rich Arab states, who pledged $250 million a year to the organization in 1979. An additional $4 million to $8 million is estimated to come from taxation of Palestinians, notably in Kuwait and Algeria, and from individual contributions.

But the total PLO budget is believed in recent years to have been at least twice as high. The organization is a patchwork of different and sometimes competing guerrilla groups, some of which are funded directly by "rejectionist" countries such as Libya and Iraq. These control their own expenditures and jealously guard information on their budgets. They also procure their own weapons.

The heavy funding, and other sympathetic contributions, have brought Arafat's Fatah a long way from its early days, when it built its original arsenal by collecting weapons left on battlefields by the Arab armies after their defeat by Israel in 1967. China eventually provided some arms, but the Soviet Union in the 1970s became the principal supplier of heavy weapons. Much of the Soviet weaponry is believed to have been paid for by Arab states.

While ties with the Soviet Union are considered important because of the arms link, Moscow is said to have provided only minimal financial assistance and therefore has only minimal leverage over the PLO.

Despite their vocal public support for the PLO over the years, many Arab countries have often appeared ambivalent about the organization. The conservative oil-producing states of the Persian Gulf especially fear the guerrilla groups' capacity for disruption among their large expatriate populations of Palestinians and other Arabs. Whether they will continue to fund a dispersed PLO at previous levels is unclear.

Yet it was the Arab states themselves that founded the PLO, at a summit conference in Cairo on Jan. 17, 1964. Ahmed Shukairi, the Palestinian representative to the Arab League, became the first PLO chairman.

Under Shukairi's leadership, the Palestine National Charter was drafted, calling for the total liberation of Palestine from the "Zionist entity." But the charter did not specify how this was to be done.

Shukairi insisted that Jews who emigrated to Israel after 1948 return to their countries of origin. He was quoted as saying, "By sea they came, and by sea they shall return," a slogan that Palestinian sources say gave rise to talk of throwing Jews into the sea.

Under Shukairi, the PLO was dominated by Arab governments, notably Gamal Abdel Nasser's Egypt. This and the fact that the group's military wing, the Palestine Liberation Army, was organized on classical rather than guerrilla lines led to criticism and dissension within the Palestinian movement.

One of the dissenters was Arafat, the leader of Fatah, one of the PLO component groups. Born in 1929 to a middle-class Palestinian merchant family, Arafat first had embraced guerrilla warfare as a teen-ager when he took part in the first Arab-Israeli war in 1948.

After studying engineering at Cairo University, Arafat had joined an Egyptian Army demolition squad and fought in the 1956 Suez War. According to some accounts, he had been among the first Palestinian guerrillas, called fedayeen, recruited by Nasser from the Gaza Strip for raids into Israel.

Following the Suez War, Arafat had fallen out with the Nasser government and moved to Kuwait, where he and a handful of Palestinian friends secretly founded Fatah in 1959.

Initially Arafat and his friends had devoted themselves to fund-raising and propaganda activities. But in December 1964, nearly a year after the beginning of the PLO, Arafat created Fatah's military wing, Al Asifah, meaning "the storm."

The group's first operation, launched on New Year's Eve that year, was a failure. Four guerrillas planning to blow up a pumping station at an Israeli kibbutz were arrested by Lebanese security police before they could cross the border. The first successful raid occurred eight days later when a guerrilla unit blew up an Israeli tunnel. So it went for the next couple of years.

Fatah's prospects began to improve after the Six-Day War in 1967 when, with the traditional Arab armies defeated and discredited, the group began to attract new recruits and acquired new and better weapons.

A watershed came in March 1968, when Palestinian guerrillas fought their first serious battle with Israel after Israeli forces attacked a Fatah camp at Karameh in Jordan. Although the guerrillas took heavy losses, they were able to display two destroyed Israeli tanks after the assault and declared victory.

The battle had tremendous impact on the demoralized Arab world, and Palestinians flocked to join Arafat's group. Almost overnight, Fatah's ranks swelled from a few hundred to several thousand, and mistrustful Arab governments embraced the guerrilla group.

In the meantime, other Palestinian guerrillas began to expand their own campaigns in ways that would grab the world's attention and tar the Palestinian movement abroad for years.

Under George Habash and Wadi Haddad, two doctors turned revolutionaries, the Marxist Popular Front for the Liberation of Palestine launched its first airplane hijacking in July 1968, diverting an El Al jet to Algeria. At the time, PFLP was not yet affiliated with the PLO.

Following the 1970-71 war in Jordan, in which Palestinian guerrillas groups were defeated and exiled by King Hussein's troops, the PLO initiated "foreign operations" similar to those of the PFLP.

Its first act of terrorism was the assassination in November 1971 of the Jordanian prime minister, Wasfi Tall. The murder was claimed by a previously unknown group calling itself "the hand of Black September," a reference to the month when Jordanian troops defeated the Palestinians.

Next came the infamous attack on Israeli athletes at the 1972 Munich Olympics in which 11 Israelis were killed. In February 1973, Black September struck again, attacking the residence of the Saudi ambassador in Khartoum, Sudan, and killing U.S. Ambassador Cleo Noel and two other diplomats.

Although Fatah always has officially denied any connection with Black September, the Khartoum raid gave the first solid evidence of such a link when it turned out that the leader of the operation was Fatah's top representative in the Sudanese capital. It since has become widely accepted that Black September was a secret branch of the Fatah intelligence service.

After the 1973 Yom Kippur war, however, Fatah's policy began to change. Having regained a measure of self-respect, the Arab states conferred an unprecedented degree of legitimacy on the PLO in 1974 when an Arab League summit recognized the organization as the sole representative of the Palestinian people. This was soon followed by Arafat's triumphant appearance at the United Nations in New York.

According to knowledgeable Palestinian sources, Fatah at about this time decided to disband Black September and disavow international terrorism. The change in policy -- which did not affect continuing hit-and-run attacks against Israel -- caused or aggravated splits inside the guerrilla movement.

Among the Palestinian leaders who refused to follow the policy shift were Wadi Haddad and Sabri Banna (also known as Abu Nidal). Haddad is believed to have enlisted foreign terrorists to carry on the struggle, including Ilyich Ramirez Sanchez, known as Carlos.

Abu Nidal formed a breakaway faction called the Fatah Revolutionary Committee, which claimed responsibility two months ago for the shooting of the Israeli ambassador to London, the act that helped trigger Israel's June 6 invasion.

In 1968, Arafat's forces amended the Palestine National Charter to declare that "armed struggle is the only way to liberate Palestine." A year later, the Palestine National Council adopted the Fatah goal of "a democratic state in Palestine in which Moslems, Christians and Jews will enjoy the same rights," but rejected the idea of creating a state on only part of Palestinian territory.

The council modified this position in 1974. While reaffirming that a state on all of Palestine remained the PLO's "strategic goal," the council came out in favor of setting up a state on any part of Palestinian territory that the PLO managed to "liberate" from Israel. Analysts saw this as signaling the PLO's willingness to settle for a state on the Israeli-occupied West Bank and Gaza Strip and thereby tacitly recognize the Jewish state. But despite repeated urgings by the United States and others, the PLO never has spelled this out.

While this moderate trend was developing, the PLO's various guerrilla groups were gaining power and strength in Lebanon, where they had moved following the expulsion from Jordan.

A secret 1969 Arab agreement called the Cairo Accords gave the guerrillas the run of a swath of territory in southern Lebanon, and the organization began increasingly to resemble a state within a state.

The faction-ridden country exploded in civil war in 1975. Not only did the bloody conflict deal a serious setback to the Palestinian struggle against Israel, it also crippled the Lebanese government and further complicated the power equation by bringing in Syrian troops as peace-keepers.

In the midst of this turmoil, the PLO continued to gain power over parts of Lebanon, especially in the south, where resentment against the Palestinians grew to include many of the PLO's former Moslem allies. Many southern Lebanese accused the Palestinians of taking over homes and transforming the cities of Tyre and Sidon into Palestinian-run armed camps.

The PLO's growth also came in for internal criticism. Many talented Palestinians were alienated by the organization's evolution into an Arab bureaucracy, complete with large payrolls, administrative featherbedding, widespread incompetence and a measure of corruption, as one PLO official conceded recently.

While growing bureaucratically, the PLO was declining in its guerrilla capabilities against Israel. Palestinian attacks, which already had dropped off sharply because of the loss of Jordan as a base, declined further after the Lebanese civil war. Israeli security measures such as a double electrified fence and sensors added to the difficulty of staging cross-border raids from Lebanon.

These operations became even more limited after Israel invaded southern Lebanon in 1978 in response to an attack by 11 Fatah guerrillas that left 37 Israelis dead and 82 wounded, many of them civilians. Nine of the guerrillas, who infiltrated Israel by sea from Lebanon, were killed.

After Israeli forces withdrew three months later, the guerrillas were separated from the border by a zone occupied by U.N. peace-keeping troops and by a strip of territory controlled by Israeli-backed Christian militiamen led by a renegade Lebanese major, Saad Haddad. Cross-border raids declined almost to insignificance.

Considered more threatening than raids were occasional bursts of Palestinian artillery across the border. Otherwise, Palestinian sources maintain, the PLO had ceased to pose a serious threat to Israel long before the June invasion.

While the days of self-imposed autonomy are undoubtedly over, the organization can count some gains from its losing battle with Israel. It has won respect for battling the Israelis longer than any Arab government in previous wars, and its international standing may have been enhanced by Israel's prolonged siege.

But the new challenge -- how to recover from what may have been a mortal setback to the PLO's goal of Palestinian statehood -- remains.