The tower cranes hovering over the site of a sprawling uncompleted medical and educational complex in the pine-forested hills above this port city are idle these days. The charitable project has become another casualty of Lebanon's bitter sectarian conflict.

In broad daylight, for several days in the late spring, Christian Phalangist militiamen, in uniform and with guns drawn, descended on the site and wrested from workmen bulldozers, tractors, compressors, cars, trucks and one bus.

Afterward, the benefactor and developer of the $300 million complex, Rafiq Hariri, a Sunni Moslem whose life is one of Lebanon's most celebrated rags-to-riches stories, angrily ordered a halt to construction until all his equipment is returned. So far, meetings with President Amin Gemayel and the commander of the Christian Phalangist Lebanese Forces militia in Beirut and the intervention of the American Embassy have resulted in the return of only a fraction of the millions of dollars' worth of stolen vehicles and equipment.

Murder and mayhem are common enough occurrences in Lebanon but armed robbery, at least on this scale, is not.

The massive robberies from the site of the medical and educational complex, intended to serve Lebanon's impoverished southern region, reveal the extent of the country's religious conflicts, which have sharpened in recent months. Such divisions had the fragile government of Gemayel in crisis last week, on the precipice of another all-out civil war.

The objective of U.S. policy here is to help obtain the removal of foreign forces so that Lebanon can build a strong army and central government. But the efforts of U.S. diplomats last week were focused on bringing together Gemayel and a fellow Lebanese, Druze leader Walid Jumblatt, whose militiamen had attacked the Army and shelled Beirut's airport.

A Christian Phalangist militia official laughed as he talked about the thefts at the Hariri construction site. The equipment and vehicles were "requisitioned," he said, because they were needed to dig trenches and fortifications in preparation for a battle against the Druze in the hills south of Beirut.

But his Christian foes also indicate that the thefts were directed against Hariri himself, who grew up amid modest surroundings in this coastal city, worked his way through college in Beirut and went off to make millions building hotels and princes' palaces in Saudi Arabia in the heyday of the oil boom.

The sprawling complex he began building as one of several gifts to Sidon is in the hills 10 miles east of the city, the traditional stronghold of the Christian minority here. Christians in the area share--and Hariri denies--that the money for the project is not his but that of the Saudis, whom they hate for financing the Syrians and the Palestine Liberation Organization.

At a mass this summer, for Phalangist militiamen killed in the battle with the Druze for which Hariri's construction equipment had been "requisitioned," most of the eulogy delivered by southern Lebanon's Phalangist party chief Elias Kasabe dwelled on the medical and educational complex.

"To the big man and author of grand projects, we tell him, 'You are author of those suspect projects,' " Kasabe said. "The shells that have killed our martyrs . . . were paid for with the same money that is trying to give us illusions that he is developing the area.

"The Moslem has to prove, at least for one time, that his decision comes from his head and not from outside."

A few days later, physicians at the functioning outpatient clinic of the Hariri medical center were more than mildly surprised when Kasabe's wife brought in one of their children for treatment of a minor ailment that doctors in Sidon had not been able to cure.

Rafiq Hariri is modest about the fortune he has amassed at age 39 and the largesse he has bestowed on his native country, but not about the recognition and honors they have won him.

Proudly he told an interviewer about the award he received from the international relief agency, Save the Children, in Washington this spring at a ceremony attended by Senate Foreign Relations Committee Chairman Charles Percy (R-Ill.) and Vice President Bush. The award was for the $7 million he advanced to begin the cleanup of Beirut after the Israeli siege last summer. The project was later financed by Saudi Arabia's King Fahd.

Playing with solid gold worry beads as he talked, Hariri kept looking at his watch. His next appointment was with President Gemayel, of whom he spoke admiringly.

Of the thefts, he said, "I'm angry. I'm angry. And I have every right to be."

He did not blame Gemayel for failing to retrieve the equipment, saying the president had no control over the matter. Nor did he want to point an accusing finger at Christians.

"I will not say the Christians take my equipment; I will say some guys take my equipment, so that I will not be a part of any religion war or religious clash."

He does blame the occupying Israeli forces here, the off-again, on-again backers of the Christian Phalangists. But Hariri said he has no intention of going to the Israeli forces to seek to get the equipment returned.

"I'm ready to lose the equipment, the project, but I'm not ready to lose myself. I have to shave every morning and respect the face I see in the mirror."

When Hariri began making money in Saudi Arabia in the mid-1970s, he began his philanthropy here. With a home in Paris and business trips between Beirut and Saudi Arabia, he rarely has visited Sidon, but his colleagues suggest that he was motivated by the traditional desire of emigrants who have made good elsewhere to be recognized for their achievements at home.

He began by making contributions to his old high school that now total more than $3 million. About four years ago, he decided to make a big contribution to Sidon, and first considered rebuilding its crumbling seaport. But the area was under the control of the Palestinians then and he was unable to get the necessary government agreements.

Later, a consulting team he hired to survey southern Lebanon's needs reported that the area lacked a major hospital and suffered from high infant mortality, tuberculosis, diabetes and liver and lung ailments.

As planning for the hospital developed, the idea became more elaborate. Although the planners hoped to lure Lebanese physicians back from Canada, the United States and Europe to staff it, they encountered the problem of a dearth of nurses. So a nursing school was added to the complex.

Then came the idea for doctors' offices and housing for them and the nursing students. Hariri also remembered the time he tried to recruit skilled construction workers in Sidon for his projects in Saudi Arabia and 500 of the 530 applicants listed their occupation as driver. A vocational school was added.

Then came the idea of adding an elementary school and a college campus of the Beirut-based St. Joseph's University.

The college campus, elementary school, nursing school, some dormitories and staff housing have been built, and work on the 360-bed hospital has been substantially completed. But after the thefts, construction on an extension of the college and a dormitory for it, an extension to the elementary school and the vocational school was halted.

Although an outpatient clinic has opened and the first patients were admitted to the hospital this summer, plans for its full-scale operation have been postponed.

There have been problems in recruiting doctors from abroad because of Lebanon's continuing conflicts, and because of the complex's difficulties with the Phalangists that began nearly a year before the thefts.

After the Israeli invasion in June 1982, the Christian Phalangists, who had stayed underground until the PLO was rooted out, suddenly appeared armed and in uniform in the hills around Sidon. Apparently lacking barracks for their militia, they seized the staff housing of the hospital and the nursing school's dormitory. In September, after long protests by Hariri's aides, they finally moved out. There was extensive damage to the furniture and buildings when the militiamen left.

A couple of months later came what the complex directors refer to as the "palm trees affair." Landscapers working on the grounds around the hospital and college campus decided to plant palm trees. The Phalangist militiamen uprooted them and carted them off, saying that palms were Saudi Arabian trees and that cedars, the Lebanese symbol from its northern Maronite Christian heartland, should be planted instead.