White House press secretary James S. Brady remained in serious danger of new brain pressure and infection yesterday, despite a five-hour operation Wednesday night to try to repair a sudden problem.

The problem was unexpected growth of an abnormal airway along the bone-shattered path of the bullet that struck him March 30. The airway caused pressure on the brain and a worrisome period of sluggishness and sleepiness for Brady on Wednesday.

It will take "several days of careful monitoring" before the surgery's effectiveness can be accurately determined, George Washington University Hospital doctors cautiously told the White House.

Too much air pressure on the brain can cause brain damage if it continues too long. Outside air also carries bacteria. "The risk of infection is less than before" because of Wednesday's night's repair, but "it's still there," Dr. Dennis O'Leary, George Washington medical spokesman, said in an interview.

Hospital sources added comments such as "brain injuries of any kind are a risky business" and "a danger is infection and a brain abscess -- this patient is by no means out of the woods."

However, the White House said that Brady's doctors reported yesterday that he "remained in satisfactory condition," with normal vital signs, including temperature. He slept intermittently Wednesday night, "but he is readily awakened and responds normally to questions," his doctors reported.

O'Leary said the fact that Brady was shot with a "Devastator" bullet -- designed to explode on impact -- might be responsible for his latest medical problem.

The doctor termed it a "reasonable thesis" that the "Devastator bullet might have caused a little bit more damage in this bony area," and said the bullet's heavy impact on the internal bone structure is a strong indication that "the Devastator device did go off on this bullet, although we'll never be able to determine for sure."

Brady's problem airway might have started growing only hours before his attendants noticed his lack of responsiveness Wednesday, after days of increasing alertness and even some zest, as well as normal periods of anger and discouragement.

A brain scan with a computerized X-ray device that assembles single, life-like pictures from many views revealed what had happened.

According to O'Leary, the new damage "was right in the pathway" of the March 30 bullet; that is, through Bray's left temple and the left side of his skull, passing through and shattering his frontal sinus (sinuses are air-filled openings enclosed by thin areas of skull bone), then through the smaller ethmoid sinuses, then through the dura or tough coat of the brain, and into the left tip and on through the right side of the brain, carrying in enough air from the nasal passages to have an effect on the brain.

On March 30, O'Leary explained, "there was a lot of shattered bone" -- skull and sinuses -- and neurosurgeon Arthur Kobrine, in a 6 1/2-hour operation, "packed that area with muscle and did all he could at that time. He did the best he could, but he couldn't do more without spending a number of additional hours."

"That wouldn't have been good for his patient," then in great immediate danger of death from his gunshot wound. "So," O'Lleary continued, "I think Dr. Kobrine made an absolutely correct judgment. You're often in a sitution where you have to balance things, with the patient's best interest in mind. And there was a good chance the area would heal and seal over, as it does in many patients."

When it became urgently apparent Wednesday that it had not, Kobrine first inserted two needles through Brady's skull to remove the accumulated air and restore him to alertness.

Then, on a "non-urgent" basis but "knowing that the sooner he acted, the better off Brady would be," Kobrine scheduled the new operation for 7 p.m., O'Leary said.

Again, Kobrine slowly and meticulously "closed off the destruction, the passageway," packing it with muscle tissue "to get it as snug as he could" and try to create "a watertight seal."

Then Kobrine closed the hole in the dura with muscle fiber, "again very meticulously with lots of little sutures, carefully placed."

O'Leary said, "Only healing can really give you a watertight seal, and it will be over the next 24, 48, 72 hours that the body will hopefully take over and do the rest of the job."

The operation took much longer than expected. "As a doctor," Kobrine told O'Leary, "I don't get paid by the hour. I get paid to do it right."

The incident was Brady's second complication. Last weekend his drugs caused a high fever and rash. Both faded with new medications.

The situation is "a setback in terms of the totality of recovery," O'Leary said. Translation: it probably will take Brady longer to get well.

But it should not be a setback in "neurological recovery," O'Leary added. In other words, there probably has been no new brain damage at this point.

Events such as this, O'Leary emphasized, are not unexpected in brain injury. "Nerve tissue is delicate," he said. It heals slowly and healing is often incomplete."

He called success in this or any surgery" a combination of the talent of the surgeon and the body's ability to heal."