Col. Muammar Qaddafi, "brother leader" of the Libyan revolution, strode deliberately through the crowd of journalists in an anteroom of his military headquarters, forcing a chuckle and shaking a few hands.

He walked stiffly in his Bedouin-inspired costume, seeming to tip slightly backward, and his black eyes glowed from a face that has become noticeably lined in recent years from what is reported to be a taxing regimen of too much work and too little sleep.

Then he disappeared into an inner office whose entrance was a narrow, reinforced door, blocked off by young bodyguards with bushy Afro hairdos made popular in Libya by their leader. The journalists, many of whom had been urged to travel to Libya from various European countries for a Qaddafi news conference, were told the brother leader had changed his mind.

Some European analysts speculated that he feared the Polish crisis would push his words off the front pages and television screens, reducing the impact of his arguments against the Reagan administration. Others, however, said he simply may not have felt like taking the time, confident the television cameras would be there whenever he called them back.

According to foreigners with extensive experience here, Qaddafi, 39, deals personally with all major decisions made in the name of his five-man Revolutionary Command Council. He sleeps only four or five hours a night and as a result is reported to suffer from nervousness, they say.

In keeping with the ways of Third World revolutions, much of his work is done late at night in the military headquarters where he maintains simple offices next to his quarters in the heavily protected Bab Ziziah compound, these informants say.

"He is at his best between 10 p.m. and 2 a.m.," said one, adding that Qaddafi also rises early for Moslem morning prayers. "Yes, he is serious about that. The others, not. But he is serious about it."

Qaddafi's second wife, a nurse whom he met a decade ago when she cared for him after an appendectomy in a Tripoli hospital, lives with him in the military compound, pregnant with their sixth child, the source said.

Qaddafi is reported to genuinely fear an assassination attempt. His secretary for heavy industry, Omar Mustafa Muntasser, recently responded to questions about Libyan assassins by recalling U.S. Central Intelligence Agency attempts to kill President Fidel Castro of Cuba.

Qaddafi's wife personally supervises his care, including administering any medicine, a well-informed source said. Qaddafi's prescriptions are renewed more frequently than necessary to reduce the chance of poison being introduced, he added, recalling that Qaddafi told a television interviewer recently of alleged U.S. attempts to "poison my food."

Qaddafi meets frequently with the other four members of the ruling Revolutionary Council, who are said to be vividly conscious that their fate hangs on Qaddafi's. "They are very much aware of the fact that they will all stay together or all go together," said a European diplomat.

With his personality, charisma and historical role, Qaddafi is completely in charge and frequently rides roughshod over the other council members, he added. Another informant said Qaddafi has on at least one occasion slapped former Prime Minister Abdel Salam Jalloud, a member of the Command Council, because orders were not carried out adequately.

Although at least one attempted military coup has been reported in the past year, Qaddafi shows no outward signs of fearing his people. Diplomats who watch his actions closely say he still drives his own Peugeot around Tripoli from time to time without heavy protection.

Dissatisfaction is reported high among merchants whose livelihood was affected by a September order abolishing private trade even in small shops. The reported coup attempts indicate some army officers also may be unhappy with Qaddafi's style of leadership. But in conversations with foreigners at least, several Libyans expressed pride in Qaddafi's economic achievements such as public housing and school building.

"Of course, we all love our leader," a Libyan professional said with a smile after a Friday afternoon conversation on a Tripoli beach.