"American Idol" ends on low, questions over future

* "American Idol" finale lowest TV ratings since 2004

* Season 8 ends with future of 3 judges in doubt

(Adds Randy Jackson, Ryan Seacrest contracts, line 34)

By Jill Serjeant

LOS ANGELES, May 21 (Reuters) - Kris Allen's upset victory over glam rocker Adam Lambert drew the smallest "American Idol" finale audience since 2004, slowing the television ratings juggernaut and raising questions about the future of some of its key players.

Preliminary figures from News Corp's Fox network on Thursday showed an estimated 28.8 million people watched the two-hour finale of the popular TV singing contest on Wednesday, down from 32 million last year.

While still America's most watched TV show, "American Idol" audiences have slipped to an average 26.3 million per twice weekly episode over the five-month broadcast, compared to a 2006 high of about 30.8 million.

The slide came despite producers adding a fourth judge, Kara DioGuardi, to keep the show fresh. DioGuardi, a songwriter who helped pen the poorly received first single "No Boundaries" for Kris Allen, now must wait to hear whether her one-year contract will be renewed.