WASHINGTON - A U.S. military report on deadly air strikes in Afghanistan calls for better training for air and ground forces to reduce civilian casualties that have undermined the counterinsurgency campaign, the Associated Press has learned.

The recommendation on training and a second one urging a review of the use of air support are among a half-dozen findings in an unreleased report on a May 4 bombing that was aimed at Taliban extremists but also killed dozens of Afghan civilians, two Defense Department officials said yesterday. They spoke on condition of anonymity because the report has not been made public.

A separate recommendation is to review aircraft used for air support that troops call in to back them up, officials said.

The report says that U.S. air and ground forces headed to Afghanistan should receive advance training in the kinds of scenarios they could face, including situations that have resulted in civilian deaths, one official said. The report suggests periodic refresher training throughout troops' tours of duty in the war zone, meaning that forces would get training early and often to reinforce battlefield tactics.

The Obama administration is sending 21,000 troops to Afghanistan to bolster the nearly eight-year-old campaign. That will bring the total foreign force there to about 68,000 Americans and 33,000 allied NATO forces by the end of the year.

Defense Secretary Robert M. Gates and other top military officials have said that reducing civilian deaths is crucial to winning Afghan support for American and coalition operations against the insurgents and boosting the population's support for the central government.

Canadian Brig. Gen. Richard Blanchette, a spokesman for NATO forces in Afghanistan, said the review would help international forces improve their operations.

"This will close the loop of what needs to be done to have the right kind of learning process," Blanchette said in an interview from Kabul.

Blanchette also said, as a number of commanders have, that some of the deaths in Afghanistan were the direct result of the insurgents' intentional practice of hiding among civilians. He said that using civilians as human shields was designed "to discredit the action of our forces," and making the jobs of young field commanders "very tough" when they have to call for close air support.

He declined to comment specifically on the report because it has not been released.

Afghan officials have said that 140 civilians were killed during the air strikes in Farah province. The report being prepared for release holds to earlier U.S. estimates of a lower death toll of about 30 civilians and 60 to 65 Taliban fighters. Officials acknowledged that a precise number might never be known because many victims were buried before the investigation started.