The Soviet Union has handed over valuable intelligence information that may have helped the allies hold down expected casualties in the air war with Iraq, a senior U.S. military source said Saturday.

The source, insisting on anonymity, said the United States has been "very pleased" with details the Soviets have provided about Iraq's arsenal, including its weapons and its air defense system. The Soviet Union was for years Iraq's military supplier.Details of what the Soviets turned over to the United States were contained in a story published in Saturday's Philadelphia Inquirer.

An Air Force general, who was not identified, said the information has enabled the U.S. and allied fighter pilots to counter Iraqi air defenses by adjusting electronic counter-measures on the aircraft.

Knowing the frequencies of Iraq's air defense radars is like having a sophisticated "Fuzzbuster," the general said.

The Soviet-supplied details may be one reason the allies' casualty rate is not as high as some had projected.

Estimates provided to the House Armed Services Committee before the Persian Gulf war started Jan. 16 projected a loss of 70 to 80 aircraft a week, assuming 2,000 sorties a day. So far, only a score of allied planes have been lost.

Mark Kramer, a specialist on Soviet military affairs at Harvard University, said that Defense Secretary Dick Cheney asked the Soviets to give him information about Soviet weapons when he visited Moscow last fall.

Moreover, Kramer said the Soviets could turn over information about Iraq without exposing military secrets because Moscow would have modified its equipment before selling it.

In Moscow last September, Vladimir Kryuchkov, the head of the KGB told The Associated Press that Moscow would be willing to help the CIA with military intelligence on Iraq. The CIA declined comment.