In 1981, the Air Force celebrated its second lowest major aircraft accident rate in history, 2.42 major mishaps for each 100,000 flying hours.

That rate nevertheless meant that 74 Air Force planes--at an original cost of $626 million--were destroyed, and 122 lives were lost, according to data supplied by the Air Force.

In each of the last two years, according to Pentagon data for all the services, more than $1 billion worth of military airplanes and helicopters has been destroyed in flying accidents.

Along with the loss during 1980 and 1981 of more than 400 aircraft, the services had 413 fatalities in the accidents.

Pentagon officials tend to downplay these figures, arguing as one Air Force spokesman said recently, that "the only way to stop the accidents is to stop flying."

He also said, "If you don't train in a realistic manner, a whole lot more of your pilots are going to die in a war situation."

Congress, in its search for budget cuts, is beginning to focus on the big defense budget buildup. A possible starting point might be the increasingly expensive "attrition aircraft"--planes to replace those destroyed in accidents.

For example, the administration is asking Congress to begin a program in fiscal 1983 to add 336 F14A Tomcat fighters in the next 15 years to the Navy's already programmed force, at an overall cost of $23.7 billion. According to the Navy, 246 or 70 percent of these new F14s, which are to cost an estimated $42 million each, are to replace aircraft lost in accidents.

The Navy and Marine Corps accident rate has been so high recently--112 aircraft in 1980 and 87 last year--that in one 1981 congressional hearing it was said with a bit of exaggeration that "we are going to produce fewer aircraft this year than we attrited last year."

A large number of the Navy and Marine Corps losses--41 of the 87 planes destroyed last year--take place on aircraft carriers.

The cost squeeze for the Navy comes about, as it does for all the services, because the attrition aircraft cost up to twice as much as the original aircraft being replaced.

Last year, for example, seven older F14s, which cost an average $20 million apiece, were destroyed in accidents, according to Navy data. Their replacement aircraft will cost twice as much.

At a House Armed Services Committee meeting last year, Vice Adm. Wesley L. McDonald, deputy chief of naval operations for air warfare, testified that the best way to increase the number of Navy aircraft is "to reduce somewhat the number of aircraft annually lost in the Navy's inventory."

But the admiral then conceded that this would not be easy: "Attrition, unfortunately, is more or less fixed, and I do not say that glibly. It's very difficult to reduce the attrition figures below those that we're seeing in today's world and have seen for the past six or seven years."

McDonald gave the committee a chart that projected Navy and Marine aircraft accident losses in the current year at 114. For the first three months of this year, the Navy and Marines have already lost 22 aircraft at a total cost of $109 million, a rate ahead of last year's.

An Air Force spokesman, asked about the accidents, said that training these days "is carried out in a more realistic threat environment."

To illustrate, he said that before Vietnam, attack fighter-bombers "trained at coming in at 5,000 feet, diving down to drop their bombs, leveling off and pulling away." Today it is "considerably more realistic," he said. "They are going in low and fast between 200 and 500 feet off the ground at an air speed of 500 miles per hour . . . . In peacetime we are trying to give them the equivalent of their first 10 days in combat. Unfortunately, you have losses because of the risks you have to take."

The Air Force chief of staff, Gen. Lew Allen Jr., noted in a Jan. 13 announcement that the "improved safety record" in 1981 was due in part to "the best rate in Air Force history for the fighter/attack force, which traditionally has the highest mishap potential of any Air Force aircraft because of the type of training conducted."

In the last two years, Air Force accidents resulted in the loss of 148 planes, 99 of them fighters or fighter-bombers. In that total were 39 of the older F4 fighters, which the Air Force says cost an average of $7 million apiece; six F106s at $15.9 million each; eight F16s at $9.1 million each and nine of the modern, high-technology F15s, at $18.8 million each.

As a rule of thumb, according to one Air Force official, the service buys one extra attrition airplane for each one it wants to keep in service. As another way of looking at it, the service expects "seven losses per 100,000 flying hours" as its "projected F16 attrition rate," according to an Air Force fact sheet.

The current projected purchase of F16s between now and fiscal 1990 is 1,985 aircraft. Of that number, 451 or roughly 30 percent are for attrition. The projected cost per airplane is $17.5 million, or a total of $5.1 billion for attrition aircraft.

The Army's accident losses are mainly in helicopters, 39 last year, along with three fixed-wing aircraft. There were 29 fatalities in these accidents, and the cost of the lost aircraft was $35 million, according to Pentagon figures.