If President Reagan had been taken to the White House rather than to George Washington University Hospital he could have been killed by the bullet that lodged an inch from his heart and aorta, according to the surgeon who operated on him.

Only because the president got prompt and highly skilled modern shock-trauma care was he in no danger of dying, said Dr. Benjamin Aaron, the hospital's director of chest and cardiovascular surgery.

The operation to remove the bullet was more difficult than he had anticipated, and he almost gave up three times trying to find it, Aaron said.

In a three-hour account of the events of March 30, Aaron has given The Washington Post a grimmer picture of Reagan's close call than the public received.

"If the president had been taken to the White House after he was shot instead of to George Washington Hospital, or taken to a more distant or lesser hospital, I think he would have been in big trouble," Aaron said. "He could have been another Dr. Michael Halberstam.

"We found the bullet no more than an inch from his heart and an inch from his aorta," Aaron continued. The aorta is the huge vessel that transports fresh blood to most of the body.

The bullet's proximity to the heart was reported by one radio reporter, but Dr. Dennis O'Leary, the hospital's medical spokesman, quickly denied it, and said the bullet really struck "several inches" away.

"I had a hard time finding the bullet," Aaron recalled. "Twice I almost gave up. But I had a strong feeling in my brain I shouldn't leave that bullet in the president, an inch from his heart. . . . As it turned out" -- since it proved to be an explosive bullet whose explosive was toxic -- "that was fortunate. . . . I think there's no question but that we would have had to go back into his chest again and take it out, because it might have ruptured and started leaking.

"The president," Aaron emphasized, "was never in real danger of death here, because he got first-class care from the first minute. But he needed it. He was right on the margin when he got here."

The president was on the edge of a precipitous drop in blood pressure and dangerous physiological shock due to blood loss, the surgeon said.

Did O'Leary, associate dean of the university's medical center, mislead the nation when he painted the president as a joking man, in no way dangerously hurt? To some extent.

O'Leary has admitted to some errors and sometimes having "a little bit less than complete information."

"I tried to be as upbeat as possible without damaging my credibility," he said.

O'Leary did accurately and successfully reassure the country that, barring surprises, it would have a live, functioning president. Probably few could have done as well in portraying the urgent care being given simultaneously to the president, his press secretary and a Secret Service agent, all wounded by .22-cal. Devastator bullets allegedly fired by John W. Hinckley Jr.

The president thought he had just been bruised when shoved into his limousine by Secret Service agent Jerry Parr, but Parr, seeing blood on Reagan's lips, changed course from the White House to the nearby hospital.

O'Leary said the president "probably still would have been okay" if he had had to travel another 20 or 30 minutes to a hospital.

Aaron said he thinks that "another 20 minutes and he might have been in trouble" and could have died.

At the hospital, the president started walking into the emergency room. He was pale and shaky and light-headed, and his legs started to buckle. He was bleeding internally "very vigorously . . . at a rather alarming rate," Aaron said, and had lost 20 percent of his blood volume, "closely approaching a shock state."

He was getting blood soon. He ultimately lost more than 50 percent of his blood, but the transfusions meant he was never "down" more than 20 percent, Aaron said. At that point, however, his "blood was still rolling out of a chest tube," so he was wheeled into an operating room for three hours of surgery.

"We didn't know where the bleeding was coming from," Aaron said. "But we had plenty of time, because his blood was being replaced." So an abdominal incision was made and the belly area was flushed.

"Now," he said, "we could see the dark blood welling out of the hole in the lung. The bullet's entry site in the president's side was a slit wound, but the hole in the lung was round. So the flattened bullet [which ricocheted before it hit] evidently went into the chest like a disc, sideways, then spun through the lung like a ball, turning. It tore up a lot of lung. When I found it, it was about an inch from the heart and aorta, right against the heart's surface, almost.

"I think there was some kind of Divine Providence or something riding with that bullet. Because it still had a lot of zing, and one can only conjecture how much worse things might have been."

He continued: "I wanted the bullet. You never operate to find a bullet unless you have to. But it is good traumatology to remove any foreign body, if you can. I felt where I knew from the X-ray it ought to be. I felt and I felt and I felt and I couldn't feel it."

He ordered another X-ray, because "bullets more around a lot." But it was still in the lung, and "I ultimately threaded a catheter down the bullet track" and "I finally felt it."

But "every time I squeezed it slipped and squished around. It was like trying to find a dime through a sponge. I came close to giving up and closing the chest a couple of times."

But he did not, and "finally I worked or pinched it to the lung's surface with my fingers."

The wound delineated, all damage was repaired.

What made the president's emergency care so successful is the high state of readiness, training and technological skill typical of many academic or teaching hospitals.

Aaron, too, is a new kind of doctor: a combined surgeon and specialist in physiology, biochemistry and the growing sub-specialty called traumatology. Traumatology is the harsh science of caring for the victims of violence.

This science made the response to this injury very different from that when at least two assassinated presidents died of their wounds.

Many authorities think that doctors bungled the care of James A. Garfield. He was shot in the back and shoulder on July 2, 1881, by a disgruntled office-seeker at the Baltimore & Potomac railroad station here.

He "definitely could have survived," said one authority, but doctors let him lie where he was shot for nearly eight hours, then failed to drain his wound adequately.

William McKinley, shot in the stomach on Sept. 6, 1901, at the Pan-American exposition in Buffalo, was operated on the spot by a gynecologist who happened to be near. He ignored another doctor's suggestion that he insert a drain to combat bloating and infection. McKinley died of infection five days later.

Aaron said the outlook would have been less favorable for Reagan just 20 years ago.

"We didn't have some important anesthetic techniques. We didn't have the ways to monitor blood gases and blood pressure and the other magnificant monitors we used here. People didn't have the physiological background.

"What you saw when we had these three patients in the emergency room all at once -- and a 'code' patient too, a cardiac arrest -- and all four came out all right was the spinoff of 20 years of advances."

This medical system has been built to a large extent with federal funds.

The Emergency Medical Systems Program, which helped organize George Washington's "Level 1 Trauma Center" and others, would be ended, or might not be continued by any state with limited federal block grand funds, under Reagan's cost-cutting program.

Testifying before a House health subcommittee on April 7, a panel of Washington doctors agreed that if the president had not been rushed to a trauma center there is a "high" probability" that he would not be alive.