It is beginning to look like “Extreme Makeover: ‘American Idol’ Edition.”

One day after Steven Tyler announced that he was leaving “American Idol,” the blockbuster singing competition on Fox, Jennifer Lopez said on Friday that she too would exit the show, television’s biggest of the past decade.

The two moves, augmented by speculation that the longest-serving judge, Randy Jackson, may also stop judging, have set up what could be a complete overhaul for  The changes follow a season when the show for the first time showed ratings vulnerability, dropping 30 percent from the previous year’s average.

Ms. Lopez, who joined “Idol” two years ago with Mr. Tyler, appeared as a guest by phone on Friday morning on the Los Angeles-based radio show starring Ryan Seacrest, the host of “Idol,” and tearfully told him: “I honestly feel like the time has come. I know I have to get back to doing the other things I do.”

The Fox network, which issued the news about Mr. Tyler on Thursday, seemed to be surprised by Ms. Lopez’s radio announcement. By late Friday, the network had not commented on Ms. Lopez’s remarks and said it did not plan to do so.