The brother is an impetuous officer, who wields control over the praetorian Republican Guard. The sister is nicknamed "the Iron Lady." Her husband is a burly general who rose methodically through the ranks of Syria's feared intelligence services. Presiding over them is Bashar Assad, the Syrian president who runs what some have called "a dictatorship without a dictator."

Diplomats and analysts say that together, the four represent the corporate leadership of Syria, a country facing its greatest crisis in decades following the release of a U.N. investigation that implicates senior officials in the assassination of former Lebanese Prime Minister Rafiq Hariri. In this crisis, they say, the Assad family circle is a source of the president's strength. It may also be his weakness. If his relatives are directly linked to the killing, the scandal could bring down his government.

Both Assad's brother Maher and his brother-in-law, Asef Shawkat, were named in earlier versions of the report, although many diplomats here said the evidence was spotty. The Syrian government has repeatedly denied any role in the killing.

"It is about interests at the end of the day," said a Syrian intellectual familiar with members of the government but speaking on condition of anonymity for fear of harassment. "They say, 'We have to protect our own, otherwise we will all go down together.' "

As the U.N. Security Council debates a resolution demanding Syria's cooperation with the investigation, Assad's inner circle is the focus of attention in the country, where reading the Kremlin-like tea leaves is an intellectual pastime. Many here believe any change in the government would come from within. But as long as the circle remains unbroken, many also suspect the government can endure the short-term crisis, even if few can sketch out a scenario that would end Syria's isolation.

"As long as [the family members] are not trying to act against him, it will be hard to pull off a successful coup," said Flynt Leverett, a former National Security Council staffer in the Bush administration who is now at the Brookings Institution. "That doesn't mean people may not try, but it'd be hard to pull off as long as they're in his corner."

The reliance of Syria's leadership on family is not unusual in the Middle East, where an array of authoritarian republics and monarchies have reserved strategic positions for sons, brothers and other relatives.

But interviews with Syrian analysts, diplomats, dissidents and intellectuals paint a picture of a tightknit circle that has dramatically narrowed over the five-year tenure of Assad, who succeeded his father, Hafez, in 2000. Most stalwarts of his father's rule have been forced out, many hailing from the minority Alawite clan that has buttressed the rule of the Baath Party in Syria for 35 years; one of the last, the powerful Interior Minister Ghazi Kanaan, was said to have committed suicide this month in Damascus.

Divisions are said to abound. But many analysts say those differences were set aside this spring, after Hariri's assassination forced Syria to end its 29-year military presence in Lebanon and prompted the U.N. investigation. But some Syrians blame the circle's small size for a string of foreign policy decisions in Lebanon and Iraq that have left Syria as isolated as at any time in its history.

"Nobody listens, nobody reads," said Marwan Kabalan, a professor at Damascus University and analyst at its Center for Strategic Studies. "You have a very small circle of decision-makers in charge of decisions in the country. What do you expect?"

In style and structure, the Syrian government is distinctly the product of one man, Assad's father, whose cult of personality presided over an elaborate overlay of institutions and alliances built across a 30-year reign. While Assad's leadership today relies on an inner circle, it has inherited some of the durability of that past era: The government has cultivated support within the public sector, the military, the Baath Party and a merchant class, some of whose powerful members are sons of government officials.

For key security and military positions, Assad's father relied on his Alawite community, a long-underprivileged minority along Syria's northwest coast, and in particular his own Qalbiyya tribe. But some Alawites grumble that the younger Assad has shown less of an inclination to patronize the community, even families that long represented pillars of the government.

Feeding that resentment is the perception of high-level corruption, both within the government and the families of senior officials. The Makhloof family, related to Assad through his mother, has become one of the wealthiest in Syria, with interests that span banking, Syria's free-trade zones, duty-free shops and nascent mobile telecommunications.

"The father led not only the country but also the family, the sect and the army, while, with President Bashar Assad, this kind of strong leadership is not available," said Sadiq Azm, a Syrian writer teaching this year at Princeton University.

One of the most dynamic figures in the circle is Shawkat, a tall, husky general with black hair and a mustache. Since February, he has run Syrian military intelligence, the institution that keeps the closest eye on threats to the government. He is a natty dresser, known for expensive tastes. A diplomat recalled that at one function for Assad's father, he was the lone person not wearing a military uniform. He chose instead an expensive Italian suit, the diplomat said. Those who have met him describe him as confident, businesslike and security-conscious, imbued with street smarts that came from his rise through the intelligence ranks.

Hafez Assad's oldest son, Basil, opposed the marriage of the divorced Shawkat to Bushra, Assad's only daughter. He was fully welcomed into the family only after Basil's death in a car crash in 1994, Syrians say. Diplomats and Syrians recall an incident, though unconfirmed. In the late 1990s, the story goes, Bashar Assad's brother Maher shot Shawkat in the stomach after he insulted Maher's uncle. Relations between the two, though strained, have improved, Syrians say.

As a young operative, Shawkat earned a reputation in the confrontation with Islamic activists in the late 1970s and early 1980s that culminated with the brutal suppression of an uprising in Hama in 1982.

"Asef Shawkat is the man who's done the best job at consolidating power with his own resources and his own levers," another diplomat said. Added the Syrian intellectual: "He's ruthless and very ambitious, but he knows what he's doing. He's not stupid."

Maher is Assad's younger brother, born in 1968, shorter than the lanky Assad but more stoutly built and, many Syrians say, more thuggish. A colonel in the Republican Guard, he serves as an acting brigadier, a diplomat said. He commands the brigade in the region around Damascus, the elite force that would most likely be called on to suppress any coup attempt.

He is rarely seen in public and, by reputation, has an explosive temper, leaving those around him skittish.

Assad's older sister, Bushra, a doctor, is often described as a power behind the throne, promoting her husband's ambitions as well as her own. Strong-willed and tough, she might have been her father's choice as successor had she not been a woman, one Syrian said.

Five years into his reign, Assad himself remains liked in Syria, and people often make a distinction between him and the unpopular government. He has shorn his rule of the iconography so familiar to his father and goes out in public with his family. To many younger Syrians, he and his wife, Asma, the daughter of a renowned surgeon from a prominent Sunni Muslim family, represent a more modern vision of Syria. She was born, raised and educated in Britain, where she worked as an investment banker.

Bashar studied ophthalmology in Britain. Unlike his brothers, he never demonstrated an ambition for a military or political career. But his father began to groom him as his successor in the late 1990s after the death of Basil: He rejoined the military, spearheaded an anti-corruption drive and was given day-to-day control over Lebanese affairs.

The complaint often heard about Bashar Assad is not his personality but a lack of experience and forcefulness. Few doubt he is in charge, but diplomats say he seeks collective decisions and consensus.

"He's not a natural autocrat," one diplomat said. A Syrian dissident, who asked that his name not be used for fear of harassment, added: "Perhaps he's polite. Perhaps he's not as fierce as his brother and brother-in-law, but he's weak."

There's an adage in the Middle East: If the government survives a crisis, it can claim victory. Iraqi President Saddam Hussein did so after the 1991 Persian Gulf War. So did the elder Assad's government after the 1973 Arab-Israeli war. Diplomats and Syrians say the Syrian government's working logic in this crisis is survival. But they said the diplomacy so far adopted -- making measured concessions -- may be outdated today and more in tune with a Cold War world, where Syria could rely on its Soviet ally and a more restrained U.S. policy.

"What pushes them together is their family ties but also the awareness that they have to stick by each other in order to perpetuate their power," said Murhaf Jouejati, director of the Middle East Studies Program at George Washington University.

Since the waning days of Assad's father, stalwarts of the old guard have fallen away, further focusing power in the hands of the inner circle. One Syrian intellectual said he had often heard complaints by senior intelligence officials that they were being marginalized. That the complaints come from Alawite officials is significant, diplomats say.

The death of Kanaan, the interior minister, was perhaps the most spectacular change. The Syrian government declared it a suicide; accounts differ in Damascus, but most often elaborated is the view that he was forced into suicide under threat of disgrace. His death Oct. 12 removed the sole figure that many analysts believe represented a potential alternative to Assad's rule.

To many analysts, the narrowing of the circle has played to the benefit of Shawkat, who is seen as having most successfully built his own networks of influence within the intelligence and military.

"Everything's happened to the advantage of Asef. He's pushed away all the strong men," said the Syrian intellectual familiar with figures in the government. "The field is empty now, and that will fit him more."

In that milieu, a U.N. investigation that directly implicates officials such as Shawkat would drive to the very heart of the regime's survival, diplomats and analysts say. Most see a decision by Assad to turn against the inner circle as a red line that cannot be crossed.

"He does not have the power," the Syrian intellectual said.

Wright reported from Washington.

In an undated official portrait, Syrian President Hafez Assad, who died in 2000, sits with his wife, Anissa Makhloof. Behind them are their children: Maher; Bashar, the current president; Basil, who died in 1994; Majd; and Bushra. Maher, Bushra and Bushra's husband make up Bashar Assad's inner circle and wield considerable power, analysts say.