The uprising began as a seemingly parochial feud over a lucrative toll booth set up by right-wing Christian militiamen about 30 miles north of Beirut on the coastal highway to Tripoli.

But it evolved into a growing rebellion against the leadership of the Phalangist Party, which since its foundation half a century ago has been dominated by the family dynasty of the late Pierre Gemayel.

In the course of six days, this action of charismatic Christian militia commander Samir Geagea is now being described by its rhetorical advocates and armed enforcers as a "Christian revolution" destined to change the course of history in war-ravaged Lebanon and perhaps in the entire region.

The rhetoric notwithstanding, the balding, 32-year-old Geagea's mostly bloodless coup d'etat in the mainstream Christian Phalanists' Israeli-equipped militia, the 6,000-man Lebanese Forces, and his seizure of control of most of the Christian heartland east and north of Beirut, indicate more than just another dissident political movement.

Already, Lebanon's Christian community of approximately 1.5 million people -- less than half of the total population -- has divided, and the Phalangists have lost the protection of their private army. The rebellion has alarmed the Syrian government and placed Lebanese President Amin Gemayel in his most precarious position since he succeeded his brother Bashir, who was assassinated in 1982.

The week-old mutiny, said Moslem Prime Minister Rashid Karami today in a special radio broadcast, threatens to "undermine Lebanon and terminate its existence." The result, Karami said, could be the partition into sectarian ministates, long a dream of extremist Christian leaders and a nightmarish prospect for Lebanese nationalists.

Moslem nationalists warned the rebel Christian militiamen today to back down from their revolt against Gemayel's pro-Syrian policies, saying their actions threaten to partition Lebanon.

Shiite Moslem leader Nabih Berri said that if the revolt continued it would either bring the country to "cantonization" or a violent reaction from Lebanon's Moslems. Druze leader Walid Jumblatt also has warned of a partition move, threatening that Moslem forces would "break the necks" of the Christian rebels if they continue their movement.

Indeed, the backers of what is now popularly called the "movement to reassert the independent Christian decision" are openly advocating a federation or confederation of sectarian-based ministates, each defended by its own army and represented in a vastly weakened central governing body.

"In the long run, I think we are going altogether in this direction. If you read the situation now, the de facto situation, it would be difficult to see the Lebanon of 1943 being assembled," Fuad Abu Nader, commander of the Lebanese Forces, the largest Christian militia, told reporters yesterday. He added, "After 10 years of civil war in Lebanon, we are going to see a new political order."

Lebanese nationalists say they view such a prospect as nothing less than partition -- even though Lebanon for all practical purposes already has been demographically subdivided into sectarian cantons of Christianity and various sects of Islam -- and warn that it would spell the end of a viable Lebanon.

Syria, which long has dominated Lebanese politics, is avowedly determined to avert such a drastic political change and has deployed at least three armored units in intimidating fashion just north of the Christian heartland that begins at Barbarah village, south of Tripoli on the coast road.

In Damascus, Defense Minister Mustafa Tlas has warned that orders have been issued to Syrian troops in northern Lebanon to advance to Beirut to bolster the Syrian-backed national-unity government if it is further threatened by the Lebanese Forces rebellion.

If the Syrians opted not to move their forces south toward the Lebanese Forces stronghold in Jounieh, they could get their allies, such as Suleiman Franjieh's militia in northern Lebanon or the Druze militia in the Chouf Mountains, to act as surrogate forces and shell Lebanese Forces positions around Beirut.

Geagea launched his armed revolt March 12, the day after he was expelled from the Phalangist Party for refusing to abandon the checkpoint and toll booth at Barbarah. He has shown no sign of wavering under the Syrian warning, although some of his top advisers have become less strident in their defiance and have begun to speak more often of a negotiated settlement.

However, the Christian rebel leaders who make up an eight-man emergency committee of the Lebanese Forces have announced plans to create a "Christian national council" that would function as a legislature to govern the Christian enclaves.

The committee vows to retake a pier in Beirut's harbor that, along with the Barbarah toll station, provided the militia with revenue.

Karim Pakradouni, a member of the committee and former confidant of Bashir Gemayel, said yesterday, "Within a few days we will proclaim a constituent assembly of the Christian National Council." Other strategists in what is known as the Christian Decision Movement said, however, that it was unlikely such a provocative move would be made in the current atmosphere.

An adviser to Geagea, who asked not to be named, said: "What we are doing is trying to reconstitute the party as a first step. Whether the Syrians will allow this to happen depends upon how we act. But first we have to demonstrate popular support. If the Syrians see we have popular support, they won't intervene, perhaps. But if one day we went to Baabda the presidential palace outside east Beirut and took over the government, the Syrians would have to act."

When asked what outside help the Lebanese Forces might receive in the event of a Syrian attack or artillery bombardment of the Christian port city of Jounieh or even Christian east Beirut, the aide replied, "We are very conscious of the fact that the West and Israel are out of this, and we can rely on nobody to come to our rescue. We are alone."

However, he said, Syrian military intervention certainly would unify all of Lebanon's Christians around the Christian Decision Movement and the Lebanese Forces and drag the Syrian Army into what he termed "a Christian Vietnam."

The aide said, "There would be a guerrilla war. Christians would throw stones and attack worse than the Israelis found in south Lebanon. I don't think it will come to it, but if necessary we are going to fight. It may be worse then they expect."

How much popular civilian support is behind the movement led by Geagea is not clear. He is a one-time medical student who is openly Christian supremacist and boasts of leading the squad that assassinated Tony Franjieh, his wife and infant daughter along with 33 of their followers at the summer home of ex-president Suleiman Franjieh in 1978.

While the rebel movement is publicly associated with Geagea, some Christian political leaders maintained in interviews that the real force behind it is Elie Hobeika, the Lebanese Forces intelligence chief who is known for his close ties to Israel. Hobeika was linked to the massacre of Palestinian civilians in Beirut's Sabra and Shatila refugee camps in September 1982.

Gemayel's seemingly malleable relationship with the Syrians and the increasingly dominant Syrian role in Lebanese politics has cost him some support, as evidenced by increasingly popular and disparaging "Amin" jokes passed among Christians in east Beirut, and by occasional portrait posters that have been defaced.

One influential Christian leader in east Beirut said Geagea had gained support after Gemayel's popularity waned as a result of "decisions that ran against the grain of the community, including the abrogation of the May 17 accord on Israel's pullout from Lebanon."

Moreover, the Christian leader said, "if Gemayel turns even more to the Syrians for support, his popularity will continue to decrease. If he depends on the Syrians to save him militarily then we would all have to fight the Syrians. Even people like us who have been neutral will have to fight the Syrians," he said.

Meanwhile, Lebanese troops were reported to have fought unidentified gunmen near a fishing village outside of Sidon today and later to cut roads leading to several Christian villages.

State-run Beirut radio said the gunmen were members of the right-wing Christian Lebanese Forces militia, but this could not be immediately confirmed.