The network described Harris, 39, as one of the "most respected young talents" in broadcasting.
Page, a 28-year broadcast veteran, told his hometown Indianapolis Star he was "terribly disappointed" by ABC's move.
"I love doing the Indy 500," said Page, 59, who will handle other sports duties for ABC and ESPN. "It's all I ever really wanted to do."
It was the second time ABC pulled Page from the broadcast booth. Page joined the broadcast in 1988 and was replaced with Al Michaels in 1999. Page returned as the Indy 500 voice in 2002.
ABC, which has broadcast the Indianapolis 500 since 1971, struggled throughout the 1990s with declining ratings that hit their lowest ever last year.