White House press secretary James S. Brady has suffered a new complication that could mean more brain surgery and what one doctor yesterday called a long, hard future course."

Brady's doctors said they are "still optimistic," if also still guarded, because "most patients in his condition will recover."

Brady's new problem seems to be a sometimes open, sometimes shut air passage from the sinuses or air-filled cavities in his skull to his brain. This creates a new danger of harmful air pressure and, worse, infection in his healing brain cells.

He has been restricted to his bed at George Washington University Hospital, where his most strenuous activity since being shot March 30 has been sitting in a chair for two hours. His bed will be tilted at a 20-degree angle for 19 days to two weeks to keep his head high and minimize the risk of air flow from the sinuses to the brain.

Brady's state was described as "alert" and "satisfactory" yesterday, seven days after a hastily scheduled five-hour operation to repair an earlier air passage inside his wounded skull. That passageway, along the path of the explosive bullet that struck him, was sealed.

Brady's doctors reported yesterday that on Monday night, while he was drinking iced tea, he "leaked approximately four drops of fluid from his nose."

This was an immediate alarm signal, "Because of the possiblility that this might be spinal fluid," a White House statement said, "a skull X-ray was obtained." It showed "a slight increase in intracranial air [and] an additional potential abnormal communication" or passage in "an area which could not be adequately exposed during [last week's surgery] without compressing the healing brain tissue.

"Because there is a reasonable expectation" that the newly troublesome area will heal on its own, the statement added, Brady must stay in bed to "minimize the risks of recurrent leakage" of spinal fluid or entry of air.

Then, the statement said, Brady's activities will be increased gradually, and "if there is evidence of additional leakage . . . further diagnostic studies will [asses] the potential need for further surgery."

What this means, explained Dr. Dennis O'Leary, George Washington medical spokesman, is that "we may have a long, complicated way to go, but we think he's going to make it. It's not gloom and doom here."

It is also not all cheer. The new airway apparently can open under pressure, such as that of a sneeze or movement, and admit air from the skull's ethmoid sinuses through an apparent rip in the brain covering.

This problem apparently was there, but unreached, during Brady's surgery last week.

"What we're dealing with now," O'Leary said, "is something on the bottom of the brain. it's not something you can see without lifting the brain and compressing the frontal lobe. That's not something you want to do."

Brady neurosurgeon, Dr. Arthur Kobrine, said "the vast majority of patients do heal over," O'Leary reported.

"We all anticipate that we'll get to the place where he walks with a can," but this probably four to six weeks away now, O'Leary said.

And one or more operations could be needed, hospital sources said, if the old and new air passages do not heal in short order.

O'Leary said Brady is reading newspapers, watching television and conversing, often at length, "when he feels like it."