Maj. Saad Haddad, the cashiered Lebanese Army officer who has made himself potentate of the Israeli protectorate he calls "the Republic of Free Lebanon," never just enters a room. He takes it by storm with the force of his personality and all the machismo he can muster.

His Israeli-supplied jeep skids to a stop in front of the slightly dowdy Arazim Hotel here, its long radio antennas furiously whipping to and fro. Haddad practically bounds from it into the hotel lobby, hitching the automatic pistol on his hip and throwing a bear hug around an Israeli colonel who is liaison officer to the Christian forces in southern Lebanon.

Trailed by an entourage of Israeli officers, Haddad strides into a dining room filled with British delegates to an Israel Bonds convention in Jerusalem and makes a fervently patriotic speech. Using an oversized mounted map that he leaves in the hotel for such occasions, he points to Palestinian guerrilla concentrations nearby and warns that they are a constant threat to Isreal's existence.

Then, signing his last autograph on a flag of his "republic," Haddad turns to two visitors and offers a more humble side.

"I'm a normal human being. I'm a simple officer. I do not consider myself a political leader, but I am forced to talk politics," he says.

While the question of whether or not he is normal is a matter of dispute among the various belligerents in war-torn southern Lebanon, Haddad could hardly be called just a simple officer.

He is the military commander and undisputed boss -- under Israeli tutelage -- of a very important slice of Lebanon. He is also a larger-than-life figure not only to the nearly 100,000 Christian and Moslem Lebanese who live there, but to what remains of the Lebanese central government, the neighboring state of Israel and the nations who have sent troops under the U.N. flag to try to restore order after five years of chaos.

Haddad is feared, loathed, derided, dismissed as a martinet, respected, revered as a patriot and held as the savior of a minority population that sees itself threatened with extinction.

When New York Mayor Edward Koch recently visited here and talked with Haddad, he said he had "never met a man as brave or admirable," and he stood by proudly as the major was feted in Haifa with what one Israeli newspaper described as "all the pomp and circumstance usually reserved for foreign dignitaries."

But an official of the U.N. Interim Force in Lebanon called Hadded a "dangerous madman," and an Israeli military correspondent described him as "neurotic," saying, "We're on tenterhooks waiting for the next of madness. . . . We have created a Frankenstein."

Haddad may be a strange man, but the enclave he controls in southern Lebanon is even stranger.

The flag of his "Republic of Free Lebanon" has a green cedar of Lebanon sewn next to the blue Israeli Star of David. Although it is actually still sovereign Lebanese territory, Israeli currency is exchanged almost as freely as in Tel Aviv and Lebanese shopkeepers there effortlessly speak Hebrew. Haddad's soldiers draw their pay from the Israeli Army and wear Israeli uniforms, carry Israeli rifles and drive Israeli jeeps and armored vehicles. At least a dozen Israeli-constructed roads just deep into the enclave from the frontier.

U.N. officials estimated that on any given day, as many as 300 Israeli troops are in southern Lebanon and they conduct extensive night patrols in the enclave.

Haddad, who trained at Advanced Infantry School at Ft. Benning, Ga., wears a Lebanese-style Army uniform but his men wear Israeli Army fatigues and many of them do not even bother to remove the Hebrew inscription.

Last fall, Haddad led a contingent of his troops through Jerusalem streets in Israel's annual Jerusalem March. His presence in the parade evoked sharp criticism from Israelis who oppose their government's Lebanon policy.

Just five years ago, Haddad, now 43, was an obscure Lebanese Army captain, a Greek Catholic from the southern Lebanese town of Marjayoun, with a long history of fighting Palestinians. He was wounded in the chest in 1968 during the first clash between Yasser Arafat's guerrillas and the Lebanese Army, and had developed a deep hatred of the Palestinian fighters.

By his account, he was ordered by the Lebanese government to go to the south and take control of the eastern-most of what then were three Christian enclaves that eventually were merged into one. He said he traveled by boat from the Lebanese port of Jounieh to the Israeli port of Haifa, since that road was controlled by the PLO.

"I never expected this to last so long. I thought it would all be over in a few months," said Haddad. "When I came, I thought I was making a sacrifice for my country. I followed orders 100 percent, as a disciplined soldier, and I am still following them." Nonetheless, Haddad was dismissed from the Lebanese Army after declaring the enclave an independent state in April 1979.

It is not just Haddad's personality that gives him a reputation, particularly with the U.N. force, whose radio traffic he often interrupts with odd and wrathful comments, of being a kind of King Lear, threatening the terrors of the earth from his little Ruritania. It is the frightening roar of his heavy artillery -- mostly Soviet-made 130 mm cannon Israel captured from the Arabs and gave to Haddad -- and the unpredictability of where it will be pointed.

Since the U.N. peacekeeping forces arrived in Lebanon in March 1978, they have recorded hundreds of incidents in which Haddad's units fired on U.N. positions. Twice they fired on the U.N. headquarters in Naqura, most recently in April 1980, when a U.N. hospital was severly damaged and four helicopters destroyed. Troops firing at close range with jeep-mounted machine guns demolished 15 buildings as the U.N. soldiers stood by.

U.N. positions throughout the enclave have been fired on regularly by Haddad's artillery, and unarmed observation posts have been looted and the U.N. observers beaten by the Christians.

The most grisly incident occurred last April after the killing of a militia youth in a confrontation with Irish U.N. troops. Haddad's militias ambushed a U.N. convoy and turned its Irish drivers over to an angry crowd of townspeople in Bint Jbail. Two of the drivers were shot to death and a third seriously wounded.

U.N. officials have charged that an Israeli liaison officer has been present on many occasions when Haddad's troops incited Christian civilians against U.N. forces.

The U.N. forces, in an attempt to avert incidents with the many various contestants in southern Lebanon, have equipped all the belligerent forces with radios with U.N. wavelengths. But U.N. sources said Haddad never answers his radio when the U.N. calls.

Haddad's occasional petulant shelling of civilian targets is often accompanied by demands or threats he issues over the private, American-run "Voice of Hope" radio station.

On March 20, 1980, Haddad ordered his artillery to shell Sidon, paralyzing the normally bustling Lebanese port city. The major said there would be more attacks on Sidon if a branch of Lebanon University were not established in his enclave.

Haddad has shelled Nabatiyah because electricity to his enclave was cut -- by his own artillery, it turned out -- and because Lebanese Prime Minister Shafiz Wazzer called him an "Israeli puppet."

When questioned about attacks on the U.N. force, which is not a combatant, Haddad bristled with anger.

"Why don't you ask me why 50 UNIFIL soldiers get killed by the PLO?" he demanded, lumping together all U.N. deaths, including those who died at the hands of his troops, in accidents and by natural causes.

Haddad said the two Irish soldiers were killed "incidentally" as a result of a blood feud. But animosity appears to run deep between the Christian militias and the Irish troops, whose government has recognized the PLO. Haddad has said the Irish "are primitive and always drunk," and his men refer to the Irish soldiers as "Johnny Walkers," after the whiskey.

"Our aim is to see Lebanon free, independent and unified as before," Haddad insists. "If I have a chance to liberate the last square centimeter, I will not hesitate to do it. I could take $200,000 and go to the United States and live like a dog? Why aren't the Lebanese people thankful? They do not understand the personal sacrifice I am making for the country."