The U.S. Air Force has a "secret squadron" of stolen or captured Soviet-built Mig fighter and interceptor aircraft that are flown regularly by American pilots to perfect air-to-air combat tactics. Armed Forces Journal said yesterday.

The unofficial service monthly reported in a copyrighted article that "some of the planes are very recent models; others date back to the Korean War."

"By one informed estimate, close to 20 Migs are not in USAF service," it said." Another source says the United States has maraged to obtain more than 25 planes, but has been able to keep only about five in flying condition on a regular basis."

Air Force spokesmen declined to make any comment except to say the service "has from time to time obtained, operated and tested foreign military equipment."

But other, well-informed sources said "four tofive" complete Migs in flying condition was a more accurate number than 20.

Sources said the planes were based in the Southwestern United States. They are still used on occasion to make realistic "attacks" against U.S. fighter aricraft that are en route to and from bombin missions at a southern Nevada range from other bases.

"They have about outlived their usefulness," said one source of the types of Russian aircraft now in U.S. hands, adding that Air Force tacticians would be eager to get their hands on more-up-to-dat models to determine how best to fight them.

The Journal said the Migs "are flown regularly from at least one base in the continental United States to perfect air-to-air tactics." It did not say where the Migs are stationed but aded "some are apparently available to U.S. pilots in other countries."

Publicity, the Air Force has told of training pilots in Soviet air force tactics but using their own T-38 and F-5 jets as the stimulated "aggressor" squadrons.

In addition to supplying its Warsaw Pact allies, the Soviets have sent thousands of Migs of various vintages abroad to among other nations, Iraq, Syria, Algeria, Bangladesh, Cuba, India, Indonesia, Egypt and their onetime ally China, which alone has an estimated 2,000 Mig-19s, 1,500 Mig-17s, 200 Mig-15s, and 75 MIg-21s. Ironically, egypt is now reported to have approached the United States for substitute spares for their mig-21s since cooled relations with the Soviets cut off the original supply.

"The Soviet-built planes which USAF has been operating include Mig-15s 17s, 19s and 21s," the Journal said. "They have been stolen or purloined from a wide variety of sources - defectors, friendly foreign nations and "unfriendly" ones as well."

The Mig is named after the Soviet designing team of Mikoyan and Gurevich who developed their pioneer Mig-15 sweptwing jet more than a quater of a century ago and followed through with variations up to a reported Mig-27, which is a groud attack aircraft code-named Flogger by the North Atlantic Treaty Organization and which is a modification of the Mig-23 fighter.

The U.S. Air Force didn't get any Mig-25 Foxbat interceptor inside and Force intelligence now knows the Mig-25 Foxgat interceptor inside and out.

Soviet air force pilot Vikor Belenko defeated and flew one to Japa n from Siberia last Sept. 6 Japanese and certainly American experts literally took it apart and put it back together before releasing it to the furious Soviet who hauled the plane home by boat.

Belenko, after undergoing intensive interrogation by the Central Intelligence Agency, now lives somewhere in the United States under a new identity.

"Until now," the article said, "omly one Mig-21 was known publicly to have fallen into Western hands. That one 'defected' to an Israeli air force base in the summer of 1966. Israel reportedly turned it over to U.S. intellegence authorities."

The Journal said Israel intelligence specialists "planned the defection for almost six months."

"The planning was so thorough," it said, "that an Israeli air force oficer even managed to fly a check ride with the Iraqi pilot who later defected. Israel apparently wanted to make absolutely sure that the Iraqi knew how to fly and navigate well enough that he would not jeopardize" the mission.