Col. Manuel Antonio Noriega's world snaps to attention as he walks through the drab headquarters of Panama's National Guard. Young military policemen and office workers alike seem to freeze in a stiff salute.

For 12 years Noriega has been in charge of military intelligence for the military establishment running Panama, the subject of sinister legend, fearsome and mysterious to many of his countrymen. Now, bit by bit in the year since his mentor and Panama's dictator, Gen. Omar Torrijos, died in a plane crash, the colonel is emerging from his windowless offices in the headquarters basement to assume publicly his role as one of the most powerful men in the nation-- perhaps the most powerful.

Noriega's intelligence apparatus is the entire 10,000-man National Guard. "All members of the Guard have to be in intelligence. My department is the upper part of a pyramid that collects all the information that comes from the bases," Noriega said in an interview.

Yet, for all the knowledge he has accumulated during the past dozen years, and all the power that goes with it, Noriega now appears almost trapped by his past and his position.

He has a close working relationship with Gen. Ruben Dario Paredes, who became commander in chief of the National Guard in March and now appears to have his sights on the presidency. Both recognize that while Noriega might eventually hold power as commander of the Guard, and thus be openly acknowledged as the decisive force in the country, the final distinction of the presidency is likely to elude him.

Asked if he might be a candidate, Noriega said, "No. . . . That is completely discarded."

The image of dark eminence is often reinforced by the environment Noriega has created around himself.

In his home, the 42-year-old colonel projects a strange vulnerability--pleasant, friendly, gracious but oddly shy and awkward. His house is only slightly more ostentatious than usual for the newly wealthy here and conveys a tropical ambience of easygoing domesticity. But in public the face remains reminiscent of a young Edward G. Robinson, stern and unmoving, and many Panamanians consider it frightening.

His National Guard offices are plushly decorated, full of knicknacks and souvenirs: a photo with the late Israeli Gen. Moshe Dayan, a chrome-plated Russian AK47 assault rifle that he laughingly calls a "trophy of war" without further explanation. In the waiting room there is a collection of toy toads. In Panamanian slang, a sapo or frog is a government informer. Paintings of big-eyed children in tears make up another collection.

Even Noriega's conversational metaphors conjure up disturbing images. Asked what the greatest threat to the future of Panama is, he said, "Social injustice. Social injustices are like a damp corner where there may grow poisonous mushrooms, and mold, and evil odors."