"This guy had a very serious wound. And it's not uncommon for a postoperative course [like his] to have its up and downs."

Dr. Dennis O'Leary of George Washington Hospital used these words yesterday to try to put the latest chapter in the medical history of James S. Brady "in some perspective."

Between 9:10 p.m. and near-midnight Monday, White House press secretary Brady underwent his third operation since he was shot March 30 in the assassination attempt on President Reagan. Yesterday morning, said his doctors, he was "alert and talking" and "in satisfactory condition."

"Fortunately, he's got super care," said Dr. Daniel Ruge, the president's doctor. The third operation and the blood clots in Brady's lungs that led to it should not be a setback, Ruge said.

Still, Brady seemed caught in a pattern familiar at trauma centers, that of the grievously hurt patient who has complication after complication.

"We'd have been extraordinary fortunate not to have complications," O'Leary said. "We'd hoped the latest one wouldn't develop but it was very clearly a risk."

What became apparent to Brady's doctors Monday was that he had developed several small blood clots in his right lung. They formed in his legs and were carried through his veins and the right side of his heart to his lung. They were not life-threatening, but a large clot could be.

So Monday night the doctors opened a vein in Brady's groin and threaded a small metal sieve to a point in his vena cava -- the great vein that carries blood back to the heart and lungs -- just above his navel. Some small "nuisance" clots might still get past the sieve, O'Leary said, but any large ones should be blocked.

Surgeons had twice operated on Brady's head and brain, first on the night of March 30 and again on the night of April 22. The second operation was to seal a passage that was carrying dangerous air from the sinuses to the brain.

Brady slept well in his own room after his surgery. He had no fever yesterday and no unwanted air pressing on his brain. But the careful watch on him continued.