LOS ANGELES — Mary Hart, famous for reporting on the famous, was sitting on the “American Idol” set last month, preparing for an interview with Jennifer Lopez. The questions were poofier than her blond blowout (“Do you still feel like you’re Jenny from the block?”), but no matter. Hart did not become a tabloid television queen by pushing celebrities too far out of their comfort zones.

Lopez was already won over.

“You’ve brought so much into all our lives,” she told Hart, an “Entertainment Tonight” host whose final show is to be broadcast Friday. “There is only one Mary Hart.”

Twenty-nine years ago Hart first peppily perched herself behind the anchor desk of “Entertainment Tonight,” then a new kind of syndicated show that ushered in the celebrity television age. Although diminished in the ratings, the series still attracts an average of 5.9 million viewers, according to Nielsen — more people watch Hart each night than watch Katie Couric. The success of “ET,” as viewers call it, has inspired imitators like “Access Hollywood,” “Inside Edition” and the entire E! Channel, and helped transform once-remote movie stars into accessible celebrities.

Now 60, Hart, with her deep contact list and blindingly bright personality, has been the genre’s No. 1 ambassador. When she leaves Friday — of her own accord; she was not pushed — she will be another sign that celebrity-oriented television is undergoing a generational changing of the guard, with Oprah Winfrey and Regis Philbin leaving the stage, and Barbara Walters giving up her Oscar special in February. The gentle world of celebrity journalism is fading, replaced by the Hollywood Babylon of Perez Hilton and TMZ.

Hart acknowledged as much in an interview at her bungalow on the CBS lot in suburban Studio City.

“The tone of television has changed,” she said. “A lot of people like to watch ambush TV now.” She added: “I’m proud that we don’t do that. I’m proud that we have a credibility and trust that comes both from the audience and the stars.”

But the question remains: Now that everyone is a celebrity insider, reading Lady Gaga’s Twitter feed and watching Lindsay Lohan’s every move on YouTube, is there anything for Hart and her imitators left to report?

“I still love what I’m doing,” Hart said emphatically.

She grew up mostly in South Dakota and eventually competed in the 1970 Miss America pageant as that state’s entrant. Philbin gave Hart her start, hiring her in 1981 to be his co-host on “The Regis Philbin Show.” When it was canceled in a matter of weeks, a show that had just gone on the air, “Entertainment Tonight,” interviewed her about the humiliation. The next day the show hired her.

In time, the show took off. Her girl-next-door charm delighted viewers, and her warmth disarmed celebrities. She became a star in her own right, with the ability to command attention, in Hollywood and in living rooms, like nobody else in this corner of show business.