Col. Said Musa, the Palestinian guerrilla leading the mutiny that threatens to topple Yasser Arafat, is pursuing a military strategy of bottling up and then overwhelming his opponents that reflects the classical training Musa received at Sandhurst, Britain's most distinguished military academy.

His continuing campaign against Arafat in Lebanon's Bekaa Valley has enhanced Musa's reputation as a courageous fighter and a "straight arrow" who eschews the excesses that many officers in the Palestine Liberation Organization have fallen prey to. Both qualities have brought him new recruits.

But his total rejection of any political compromise with Israel and his insistence that the Palestinians can build a military machine capable of fighting Israel in conventional terms also is provoking new debate about the true meaning of last year's expulsion of the PLO from Beirut and what some say is Musa's indirect responsibility for the Israeli invasion of Lebanon.

He also faces criticism that he is being used by Syria to cut PLO Chairman Arafat down to size and to break the PLO, criticism that carries great irony for Musa in view of his leading role in attacking Syrian forces in Lebanon during fighting in the 1975-76 civil war.

Few observers believe the rebellion Musa launched within Fatah--the PLO faction that is Arafat's power base--two months ago could have made any headway without strong Syrian support. But it also is clear that Musa, with his long-held and fundamental policy differences with Arafat, suddenly became attractive to many guerrillas after the setbacks to the PLO in Beirut and in Arafat's abortive talks with Jordan's King Hussein on a peace plan advanced by President Reagan.

Arafat's close aides fear that Musa's preference for military rather than political action will find a strong following among guerrillas and refugees who have come only slowly to the realization that the evacuation from Beirut during the Israeli siege last summer was a defeat and not the victory it was proclaimed to be by the PLO at the time.

The largely unknown officer leading the movement that threatens to topple Arafat's 15-year reign over the PLO has developed a reputation over the years among those who have known him as a tough and honest leader. In the ranks he is remembered for the way he led PLO forces in southern Lebanon against the advance of Syrian tanks in 1976 and for the four times he was wounded in 1981 in Israeli raids into Lebanon and kept springing back.

Like many senior officers in the PLO command, Musa, 56, served in the Jordanian Army and was singled out to be sent to Sandhurst. He defected to the PLO in the 1970 Black September civil war in Jordan, after refusing King Hussein's order to suppress the guerrilla uprising.

Even the staunchest Arafat loyalist grudgingly mentions Musa's rapport with fighters and his courage and professionalism that earned him loyalty and respect up and down the ranks when he fought under Arafat.

Indications are that his present reliance on Syria for military backing is an uncomfortable irony for Musa, who has tended to shrug aside suggestions that the Syrians might be using him against the PLO.

"Any Arab country that supports me in this will be an ally and not someone out to use us," he told a small group of reporters in a rare interview the day after his forces, with the backing of Syrian tanks, scored the first of their dramatic takeovers of key Arafat positions last month.

But the Syrians have signaled clearly that their intent is to promote Musa as a challenge to Arafat's leadership and his insistence on the independence of the Palestinian movement.

Accorded a privilege never granted Arafat, Musa recently spoke for 45 minutes on Syrian television. And Syrian forces surround Musa's headquarters in Lebanon's Bekaa Valley.

But Musa's dissent seems not to have sprung from the promptings of the Syrians or anyone else. For nearly two years, he had been a lonely critic of conditions in the PLO, a straight arrow in the years when the PLO ruled West Beirut, had strongholds throughout southern Lebanon, and those who wanted it could enjoy the easy availability of pretty women, fancy houses and fast cars.

"Some who were barefooted at home came here and got a BMW, a bodyguard and a driver," said a Palestinian in Beirut who had known many PLO officers since childhood.

Another PLO insider recalled sadly that in the frenzied days of the PLO evacuation from Beirut, a number were preoccupied with getting cars and furniture shipped overseas.

It was a style the Spartan-living Arafat tolerated, much to Musa's disapproval.

The corruption and corresponding allegation of misappropriations of PLO funds had become matters of considerable concern within the guerrilla movement before the Israeli invasion and recurring themes at conferences and meetings. Yet PLO leaders were hesitant to move on the issues for fear of weakening the organization, one PLO official said.

When Musa launched his rebellion against Arafat's leadership this spring, one of the triggers was Arafat's appointment to key positions of a man with a reputation for being a high flier in Beirut and another Musa accused of performing poorly during the Israeli invasion.

But Musa's crusade has gone beyond cleansing the PLO of what he and lieutenants describe as the corruption that occurred in Beirut. It also is aimed at what he regards as a straying from first principles for Palestinians--a revulsion against Arafat's dalliances with the Reagan Middle East peace plan and the possibilities for a solution to the Palestinian problem through diplomacy.

A PLO operative recalled constant arguments within the PLO command during the skirmishes preceding the Israeli invasion in 1982 and the responses of Musa, then deputy commander of the "operations room."

"If Abu Musa was there," the operative recalled, using Musa's guerrilla name, "he would say, give them all you've got; hit their headquarters."

Arafat and others in the tight leadership who ran the PLO were far more cautious.

"I think it's that Arafat was a politician and thought of this as a political thing, whereas Abu Musa was a military man," the operative said.

"I think Arafat, for a long time, has seen that the military has very little purpose in the PLO and the military resents this, which is why they are rebelling," he said.

As the disagreements grew this spring, Arafat ordered Musa and other Fatah officers who disagreed with his policies to leave Lebanon and move to PLO headquarters in Tunis. It was then, observers now say, that Musa first began to build his alliances with other dissident Palestinian factions and the Syrians.

Musa is fond of telling interviewers that he believes that Israeli soldiers, stripped of the cover of Israel's super airpower, are no match for Palestinian fighters. But he never discusses how he proposes to strip Israel of its world-class airpower.

Musa espouses armed struggle against Israel, warfare to retake the whole of old Palestine, not just the West Bank and Gaza Strip, which Arafat, in his abortive talks with Hussein, appeared willing to settle for.

It is an argument that Arafat's close aides have feared because of its attractiveness to fighters and civilian refugees who have only slowly come to the realization that Beirut was a defeat, not a victory.

The malaise appears to have set in in earnest after the collapse of the talks between Arafat and Hussein on the Reagan plan. For Musa and hard-liners, the discussions were anathema. For others, their failure ushered in a new era of aimlessness.

In the aftermath, there has been a fitful reexamination, doubts, accusations. There are some who point the finger of blame at Musa and the Jordanian officers who they say moved the PLO away from its guerrilla operations and attempted to transform it into a regular army, which would never be effective both because of its numbers and comparatively sparse resources.

But if there is an example of where the classical military operation has worked successfully, it is in the rebel advance against Arafat loyalist positions.

An Arafat spokesman calls it "the war of the bases," bases that the loyalists have consistently lost to Musa's rebels and allies.

Musa's first conquests came without a shot. They were won by the force of his argument.

As his movement gathered steam and gained the important support of the Libyan and Syrian governments, Musa moved with Syrian tanks to positions south and east of Arafat strongholds in the Bekaa Valley before undertaking in a third phase an advance up the vital Beirut-to-Damascus highway to remaining loyalist positions.

The cease-fire has left loyalists in their isolated positions, around Kfar Zabad, between the ancient city of Baalbek and the Syrian border, in Baalbek and in a triangle north, east and south of the town of Shtawrah.

The commander of the loyalists' triangular redoubt, the key remaining Aafat positions, says he has gathered forces in what he calls a "round defense"--round because he does not know from what side the rebels will attack.