Shortly after, in June 1983, Mr. Leshem asked the Air Force if it could lend him a light plane to follow the birds as they pass over Israel for his own study. But once he and Maj. O. started talking, they realized that they were both essentially trying to get the same information.

''We gave them all our data on the migration paths,'' said Mr. Leshem, ''and we looked at their maps charting where all the collisions with their pilots were taking place, and we realized that they overlapped. Then the Air Force checked the dates when their collisions were happening, and they discovered the vast majority were in the spring and fall.''

On the basis of these discoveries, the Air Force agreed to finance Mr. Leshem and his birdwatchers in their attempt to discover the exact routes, altitudes and dates when the birds would arrive.

With the early information Mr. Leshem's bird watchers produced, aided by radar and observation from a light aircraft, the Air Force was able to greatly refine its Bird Plagued Zones - called ''Bird Protected Zones'' by the bird watchers - and to activate them on the right dates at the right altitudes. Since June 1983 jet-bird collisions have been reduced by roughly half, with no serious accidents, Maj. O. said.

Early Warning System

The bird watchers now serve as an early warning system for the air force. This spring, for example, the Israeli air force had scheduled a major training mission that needed to use part of the B.P.Z. The night before, Mr. Leshem received a report from a bird watcher in the north that a large number of raptors had settled for the night near Mt. Tabor. The next morning Mr. Leshem went up in a light plane and spotted the large flock of honey buzzards and lesser spotted eagles. He landed by 9:30 A.M. and alerted the air force to postpone the mission for another day.

''We are still learning about the air corridors and making adjustments from what we thought was the original B.P.Z.,'' said Maj. O. With the help of Mr. Leshem and a computerized data base, he said, the air force hopes to refine the information even more, to ascertain over time whether the birds come through the same route every year, whether the routes and altitudes change during the day and what correlation there is between weather changes in Europe and Africa and the timing of migrations. In this way the air force will get the most training and flight room from its scarce airspace.

For Israel's bird watchers, the support of the Air Force has enabled them to identify and protect the 475 different species of birds flying through Israel - so many birds, in fact, that the International Council for Bird Preservation, the leading bird conservation organization in the world, has decided to hold its quadrennial convention in Eilat in March 1987.

When the Israeli Air Force received its F-15 jet fighters from the American manufacturer, McDonnell Douglas, they came with tough-talking pamphlets describing the plane's capabilities. The plane's motto: ''Built to Fight Where Others Fear to Fly.''The Israeli Air Force, however, has learned from experience just how incorrect that motto could be. It replaced the motto with a slogan of its own, which has been printed on a poster that now hangs in every Israeli air base. The poster shows a fighter plane flying next to a steppe eagle and says, ''Take Care, We Share the Air.''