Tiptoeing around the carnage wrought by the explosion of a booby-trapped Mercedes in East Beirut's Ashrafiyeh district, Bashir Gemayel looked nothing if not casual with his sunglasses, short-sleeved blue shirt and tan slacks.

But the jittery bodyguards who moved at his elbows were testimony that the 33-year-old, U.S.-trained, former commercial lawyer is a man who lives with danger.

The casual Bashir, the hot-headed and ambitious younger son of Christian Phalange Party founder Pierre Gemayel, is today probably the most powerful man in Christian Lebanon. He inspires fear not only among his traditional Moslem and leftist foes but among many of his fellow Christians as well.

In fact, few doubted that the booby-trapped car that killed three civilians and wounded 15 others only several hundred yards from Bashir Gemayel's well-guarded home this week had been aimed at him -- almost certainly by Christian rivals opposed to the ruthless methods he has used recently to consolidate his power.

Gemayel's importance in the complex mosaic of Lebanese politics dates from the 1975-76 civil war when, like so many other pampered sons of the aged political patriarchs who for so long brokered their country's future, he assumed the military command of the then-ragtag militia of his father's party.

The power of command fed the young Bashir's ambitions, which have grown as his 75-year-old father, known as "Sheik Pierre," has aged.

In the four years since the end of the civil war, Bashir Gemayel has single-mindedly transformed his militia into a full-fledged, 15,000-man army. It is neatly uniformed, divided into four separate services and armed with the most sophisticated weaponry, including 40 Israeli-supplied Sherman tanks.

This military force, bigger and better disciplined than the central government's own Army, has given the young Gemayel the confidence to try to do by armed might what his politician father has never succeeded in doing by traditional political negotiations: unify the Christian community of Lebanon as a step toward forcing reunification of the divided country.

Gemayel has bludgeoned those among his own coreligionists who have resisted or opposed the Phalange's determination to be the only valid interlocutor for Christian interests in Lebanon.

His militias first warred with those of former president Suleiman Franjieh in the north, killing the former president's son, Tony, along with his wife and child in a single raid.

Early this month, Gemayel's army, now renamed the "Lebanese Forces," dealt with his other great rivals on the Christian side, the supporters of former president Camille Chamoun's National Liberal Party.

Using the sort of coldbloodedness that would win the admiration of a Mafia chieftain, Bashir Gemayel struck at Chamoun's "Tiger" militias hours after his father had negotiated a deal with Chamoun for close military and political cooperation between their two parties.

Instead of allowing the agreement to go into effect, Bashir Gemayel unleashed his army the next morning against Chamoun's enclaves in East Beirut and strongholds in the scattered seaside villages north of the city. The attack was vicious and effective. Although the operation ostensibly was aimed at neutralizing the Chamoun militia, civilians as well as combatants were killed.

In the seaside town of Safra, the worst hit, families were killed in their homes and men, women and children were gunned down as they bathed in the sea. Even immigrant Egyptian laborers were shot at their construction site.

Although Dany Chamoun, the old president's son and, like Bashir, the commander of his father's militia, had already left his Safra home for work, his Australian-born wife and 19-year-old daughter witnessed the carnage, their house was overrun and, while they were not harmed, they were threatened and made to watch Phalangist gunmen kill Chamoun supporters by setting off dynamite charges on their stomachs.

In an interview later, Gemayel said the raid was a "cure" for a sick society where inexcusable lawlessness had become commonplace. "Your General Sherman did the same thing in Georgia that we did in Safra," he said. "Sometimes you have to do things you don't approve of to preserve your nation."

Gemayel denied that he was seeking to set up a ministate in his corner of Christian Lebanon. He insisted that what he was trying to do was unite all Christian forces under one command to prepare for a "liberation war" against the 600,000 Palestinians in the country whom he blames for Lebanon's ills.

"If [Yasser] Arafat, the refugees, and the rest of the 600,000 Palestinians in Lebanon do not leave, we shall force them out," he said. "We are tired of the rest of the world trying to settle the Palestinian problem at our expense by resettling them in Lebanon."

Such threats, which have noticeably heated up an already tense and anarchistic Lebanon, prompted Arafat, the head of the Palestine Liberation Organization, to proclaim a "mobilization" of his own forces in Lebanon to meet the challenge.

While no one thinks that Bashir Gemayel is in any position to carry out his dreams of "liberation," his emergence as the "undisputed leader" of the Christians is viewed with great apprehension by Western diplomats who see him, as one ambassador put it, as "not intellectually very smart but one who can be very destructive."

The Phalangist rule within the Christian conclave has also disquieted many. The party has set its own tax collection system and rules, which rely on intimidation and fear. As one Western diplomat said, the Phalangists "are moving toward what I would consider a kind of fascism."

As alarming to some is the implication for Lebanon's political tradition of the young Gemayel's rise to power. Until the civil war, the country was ruled through a carefully constructed, if often very imperfect, series of alliances among the country's traditional clan leaders and politicians, most of whom had dealt with each other since the founding of Lebanon in 1943. Although the animosities were great, there were certain accepted rules of understanding and compromise held in common.

"What we are witnessing in Lebanon today," one worried Western diplomat said, "is the ascendancy of the Maoist notion that power comes out of the barrel of a gun. In a country as volatile as this one, that is a very frightening thought."