"National Airport," aviation safety expert Charles O. Miller said the other day, "is so dangerous, it's safe."

Miller, the former chief of the National Transportation Safety Board's accident investigation office, thus expressed the view of many in aviation: the combination of National's short runways, unorthodox down-river approach path and high volume of traffic creates an adrenaline-producing flight environment that keeps pilots alert.

What will happen, Miller wondered, if jumbo jets are added to that mix, as Transportation Secretary Neil Goldschmidt is proposing to do in his National Airport policy due Aug. 15?

"There's a point where, as hazards increase, safety increases," Miller said. "But if you go just beyond that point, the bottom drops out."

Miller's question, which he first presented in a letter to the Federal Aviation Administration, is whether jumbo jets will push the complexities of National Airport beyond that point. Those complexities include these factors:

Several times a week, sometimes as often as three times a day, a jetliner just about to land at National suddenly changes its mind and, in a roar of engines, climbs skyward to circle back into the landing pattern. The captain invariably tells frightened passengers that "there was a plane on the runway" or something like that. The occurrence is common at heavily used airports such as National, LaGuardia in New York and O'Hare in Chicago that the FAA does not keep formal statistics of how often it happens. It is not a safety issue, the FAA insists.

Twice in 1977, the captains of passenger-carrying Boeing 727s elected to abort their takeoffs from National's main runway. Both times it was raining; both times the airplanes rolled to halts in the mud just off the north end of the runway a few feet from the Potomac River.

After the incidents the runway was regrooved to increase traction and airport officials speeded their efforts to build a still-unapproved 500-foot overrun for the runway.

A jetliner captain's favorite approach to any airport is a nice, fully instrumented endeavor where he can line up straight with the center of the runway from a long way out and just follow his instruments and his nose to touchdown.

National's down-river approach presents none of these niceties. To reduce noise, and to avoid flying over the White House and through the Washington Monument, planes landing to the south snake down the Potomac River, glide to the left just over the Tidal Basin, then make a hard right turn on top of the 14th Street Bridge to line up with the runway and touch down. Instruments are of no help once planes have passed the Georgetown Reservoir, because the instruments available now work only on straight-in approaches.

The Federal Aviation Administration, which works for Goldschmidt, has not adequately tested the question of whether jumbo jets can fit conveniently and safely into this mix, Miller said. "They haven't tested it, they've only demonstrated it," he said.

Only two jumbo jets have ever landed at National and they did so on crystal-clear days in 1978 when there was little wind and no other weather problem.

An Eastern Airlines A300 Airbus landed and took off three times on April 12. A United Airlines DC10 landed and took off four times on Sept. 6. On both occasions reporters and local politicians were invited to see for themselves that the jumbos could land at National and were, in fact, quieter than the planes they would be replacing.

"Wide-body (jumbo jet) aircraft operations may safely be conducted at Washington National Airport," the FAA concluded in its official report of those flights.

However, the FAA said that any airline seeking to use jumbos at National would have to fly "an initial demonstration" similar to the ones flown by the A300 and DC10, and that each pilot in command would have to meet special experience requirements before bringing his jumbo into National.

Miller would like to see testing in bad weather and testing of anticipated problems that sometimes occur in airline operations, including partial brake failures, wet runways and gusty crosswinds. "There is no way you can anticipate and test everything that could go wrong," Miller said, "but you can sure do something other than perfect-condition testing."

Despite the occasional difficulties of operating into National Airport, it has an extraordinary safety record. There has been only one fatal accident involving a commercial airliner there since the airport opened on June 16, 1941, on a site chosen by president Franklin D. Roosevelt.

That accident came on Nov. 1, 1949, when a war-surplus twin-engine P38 Lightning fighter plowed into the rear of a four-engine Eastern Airlines DC-4 that was coming in for a landing. All 51 passengers on the airliner and its crew of four were killed in what was, at the time, the nation's worst air disaster.

The fighter pilot, 29-year-old Capt. Erick Rios Bridoux, a Bolivian, suffered a broken back and other injuries, but survived. The Civil Aeronautics Board, which then had responsibility for investigating aviation accidents, charged that Bridoux was guilty of flying an uncertified airplane and that he failed to alter his course and "give way" to the passenger plane.

The CAB also said that air traffic controllers at National did not "act with requisite caution." However, the report said, this "cannot be said to have contributed to the cause of the accident." That was almost 31 years ago. h

Since then National has grown to become the 10th busiest airport in the United States and the 16th busiest in the world, despite the fact that it is virtually closed between 11 p.m. and 7 a.m.

Its air traffic controllers, by all accounts, are among the very best in the business.They can handle between 90 and 100 flights an hour on a clear day on one main runway that is intersected by the two shorter runways, which also intersect each other.

An appreciation of intensity of effort and concentration required of tower chief Harry Hubbard's controllers can be gained only by standing in the tower cab and watching. One plane clears the end of the runway, another lands on the opposite end, a third is ready to go on an intersecting runway. Radio transmissions crackle and the big jets thunder off or touch down.

Hubbard himself says he can handle all the jumbo jets you want to send him. "It's just another airplane," he said.

The Air Line Pilots Association said in recent congressional testimony that, because of National's restrictive operating corridors (up and down the river), jumbo jet flights there would present a particular problem for following airplanes: wake vortex, the cyclonic winds that spiral off the backs of the wings of all flying airplanes, then dissipate. Those winds, particularly vicious in the wakes of jumbos, require FAA controllers to maintain at least five miles separation between the jumbo and the plane following. Some pilots think there should be more separation.

Since 1970, the National Transportation Safety Board has cited wake turbulence in three airline incidents, two of them involving preceding jumbo jets. In 1972, a DC9 was on a training landing at Fort Worth, Tex., crashed as it followed a jumbo DC10 onto the runway; four crew members were killed. The other incident involving a jumbo occurred in 1975 when seven passengers were injured, none seriously, as they were knocked about the cabin of a DC8 cruising at assigned altitude. The DC8 was following a jumbo Lockheed L1011 by three minutes.

What about all those "go-arounds," those incidents where a pilot will abort a landing? Hubbard provided the estimate of "two or three times a day" as a possible frequency at National and said that many times his controllers ordered pilots to go around because something happened beyond their control: a preceding airplane did not take off as quickly as anticipated, or a landing airplane rolled the entire runaway before turning off. A go-around is "planned; it's a controlled situation," Hubbard said.

Does that mean there are too many airplanes using National? "No," he said. It could happen if just two airplanes a day used it and arrived at about the same time.

Again, the Air Line Pilots disagree somewhat. "A go-around," said John O'Brien of the pilots' association, " is not as safe as completing a landing under normal operation . . . Anytime you go around, you're increasing exposure to potential accidents."

Safety board records show that four airline accidents have occurred during go-arounds since 1970. A total of 15 people were killed and a total of seven were injured. However, the go-around itself was never the cause of the accident. In two of the accidents some mechanical failure occurred during the go-around. One accident in which 10 people were killed in Alaska involved an attempted go-around by a pilot who had apparently descended too far for weather conditions before he tried to change his mind. In the other incident, the pilot going around encountered wind shear, a sudden shift in wind currents that is particularly treacherous for landing aircraft.

There is agreement that the down-river approach is less than fabulous. The FAA is looking at two possible improvements in the navigational aids available for that approach:

Lead-in lights could be mounted on the Potomac bridges, from the Chain Bridge, through the 14th Street Bridge, to give pilots an earlier fix on the approach. Right now, there is one small lead-in light suspended underneath Memorial Bridge.

An electronic aid known as a localizer might be moved to a new location that would give pilots a better precision-instrument approach than is now available. wThe localizer presently on the airport is useless at altitudes below 1,100 feet, and the altitude of the airport itself is 15 feet.

A totally instrumented approach down-river will not be possible until the advent of the next generation of landing systems, officials said.

O'Brien said that the pilots' group supports both the lead-in lights and the new localizer.

On other questions -- short runways, brake problems, etc. -- FAA official Richard Collie said that jumbo jets are just like other airplanes. Each time an airplane flies, the pilot has to consider his load, the amount of runway available and where the go, no-go point will be.

"We are satisfied" that jumbos can use National safely, Collie said, " or we would have requested more testing . . . We feel there has been adequate evaluation."