Barbara Walters is retiring. Or maybe she’s not. In the end, I think she’ll probably have more comeback specials than Frank Sinatra. Tonight, “20/20” (8 p.m., ABC) celebrates her 25 years of service and Walters’ more than 740 interviews since 1979.

This retrospective offers a glance at the past quarter-century, but the show’s finger remains firmly planted on the fast-forward button. We whiz past snippets and clips of every president and first lady from Richard and Pat Nixon to George W. and Laura Bush. The hurried pace doesn’t allow for much introspection or information. Ronald Reagan drove a rickety jeep. Nixon wished he had burned the Watergate tapes. Why did Bush the younger drink to excess? “Because I liked the taste.” Deep thoughts these are not.

The clip show suffers from an awkwardly rigid format. We veer from the commanders-in-chief to a veritable perp-walk of the incarcerated and indicted, including Mark David Chapman (“I’m sorry”), Robert Blake (“I’m innocent”) and the Menendez brothers (they’re bad).

Do you want wacky celebrity moments? We get to hear Elizabeth Taylor cackle, and listen to Anne Heche as she speaks in the secret language of her alien masters. (Truth be told, I can never get enough of that interview.) The show reaches a crescendo of tabloid mush when Barbara trots out her interviews with the infirm and handicapped. We watch Barbara flirt with Christopher Reeve, confer with Michael J. Fox and interview a deaf and blind couple who found love at first sight, or something like that.

• “Reba” (8 p.m., WB) returns for its fourth season. Fans of old-fashioned comedies have made this the WB network’s most popular half-hour show. But I can’t help feeling that the show’s sitcom format is weirdly at odds with its subject matter.

Like many of the country tunes that singer-actress Reba McEntire made popular, “Reba” deals with divorce, misunderstanding, heartache, remorse and second chances. But every time the show’s characters approach some emotional truth, or engage in meaningful conversation, a punch line erupts followed by gales of laughter.

Tonight’s other highlights

• Julie Chen is host of “Big Brother 5” (7 p.m., CBS).
• Scheduled on “Dateline” (7 p.m., NBC): how DNA may help solve a decade-old Chicago mass-murder mystery.
• Gene Simmons returns as a cop-hating mobster in the season premiere of “Third Watch” (8 p.m., NBC).
• Four war veterans die suddenly on “Medical Investigation” (9 p.m., NBC).

Late night

President Clinton and Natalie Merchant appear on “Late Show with David Letterman” (10:35 p.m., CBS) … Jay Leno welcomes Selma Blair, Oliver Hudson, David Crosby and Graham Nash on “The Tonight Show” (10:35 p.m., NBC) … Charlie Sheen and Tisha Campbell Martin appear on “Jimmy Kimmel Live” (11:05 p.m., ABC).

Drew Barrymore and Emo Phillips chat on “Late Night with Conan O’Brien” (11:35 p.m., NBC).