Mayor Giuseppe Sala made the request following a Mass marking the 75th anniversary of the Gorla massacre, named for the quarter in the city that was struck, the news agency ANSA reported.
"I think it's necessary that the American government apologizes, knowing that we are here to forgive," Sala said, adding that he would formalize the request with the U.S. consul in Milan this week.
The air raid on Oct. 20, 1944, targeted an industrial complex near the city, but a second wave of bombers went off course and released their bombs southeast of the target to lighten their loads as they returned to base.
One bomb struck the Francesco Crispi elementary school as children raced for shelter.
"It was a very serious error resulting, as history tells us, from an incredible superficiality and inexperience," Sala said.
Copyright 2019 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.