In TV Land, the Past Is Always Present : Television: Sitcom producers aim to pump up ratings during the sweeps period by feeding the audience’s endless appetite for nostalgia.

On tonight’s “Mad About You,” Paul Buchman (Paul Reiser) seeks a TV legend to narrate a documentary he’s making on the history of the medium.

Walter Cronkite? Charles Kuralt?

He doesn’t even think of them. He goes for Alan Brady.

No matter that the egomaniacal variety show host only existed as a seldom seen character on “The Dick Van Dyke Show” in the 1960s--and has never even appeared on color TV. “Mad About You” is one of several shows that are bringing the likes of Carl Reiner back in their classic roles for the February ratings sweeps.

Ever wonder what happened to George and Louise Jefferson (Sherman Hemsley and Isabel Sanford) of “The Jeffersons”? They show up on “The Fresh Prince of Bel-Air” Monday. How about Sam Malone (Ted Danson) of “Cheers”? He goes to “Frasier” for advice on Tuesday.

And the doozy of them all comes March 1 on “Roseanne,” when Barbara Billingsley (“Leave It to Beaver), June Lockhart (“Lassie”), Patricia Crowley (“Please Don’t Eat the Daisies”), Alley Mills (“The Wonder Years”) and, once again, Isabel Sanford (“The Jeffersons”) reprise their TV mom roles.

These “Nick at Night”-inspired guest stars are a way for producers and network executives to pump up their ratings by feeding an endless audience appetite for nostalgia.

“You bring in Bob Denver from ‘Gilligan’s Island,’ wearing his white sailor’s cap, and it doesn’t matter if he’s 1,000 years old, you have instant recognition,” said Lee Goldberg, author of “TV Series Revivals” and supervising producer of NBC’s “The Cosby Mysteries.” “You don’t need to explain anything. They are members of our family. We grew up with them. It’s simple affection.”

In recent sweeps periods, “Mad About You” has featured Barbara Feldon (“Get Smart”) as an actress who starred in a TV spy series. Last May, John Astin reprised the ghoulish character of Gomez Addams from “The Addams Family” as one of Paul and Jamie’s new neighbors.

“The people who are the creative voices and forces (behind today’s shows) are also the people who grew up watching these shows,” says Danny Jacobson, co-creator and executive producer of “Mad About You.” “It’s like Old Timers Day in baseball. It’s an homage to people like that.”

On tonight’s episode, it will turn out that Paul’s Aunt Lolly was once a dancer on Alan Brady’s variety show. Through this connection, he meets the famous host, only to learn quickly what his old writers Rob, Sally and Buddy knew: that he’s a pain to work with. It’s as if “The Alan Brady Show” really existed, if only to the characters in other sitcoms.

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“That is what really intrigued me,” Reiner says. “They made Alan real, if only in the fourth dimension.”

Similarly, on “Fresh Prince,” when Will (Will Smith) and Lisa (Nia Long) go to a group counseling session, the Jeffersons (Sanford and Hemsley) are there as well. They see them as the same bickering couple, with George still calling Louise “Weezy.”

“The audience likes this because they are let in on an inside joke,” says Cheryl Gard, one of the show’s executive producers.

On Tuesday’s “Frasier,” Sam leaves his fiancee (Tea Leoni) at the altar and flies to Seattle to get advice from his former bar buddy.

“When we first started, we were a little gun-shy about having characters from ‘Cheers’ come back,” says David Angell, one of the show’s executive producers/creators. “Now we’ve established ourselves. It’s interesting to see what has happened in Sam Malone’s life, to peek back in the world again.”

Producers have long nabbed big ratings by tying up loose ends from past shows.

“The most popular question in TV columns was ‘Whatever happened to the castaways on ‘Gilligan’s Island?’ ” recalls producer Sherwood Schwartz. “There were so many I decided to do a show.”

The result was the 1978 TV movie “Rescue From Gilligan’s Island,” which topped the ratings and started a trend of TV reunion movies. Most recently, “The Rockford Files: I Still Love L.A.” and “Cagney & Lacey: The Return” each ranked in the Top 10 and helped CBS win the November sweeps. CBS brought back “The Waltons” last Sunday and will shoot for big numbers again on Feb. 23, when Jameson Parker and Gerald McRaney team anew in “Simon & Simon: In Trouble Again.”

“It doesn’t seem that long ago, but it has been,” McRaney says of their 1981-88 series. “On the USO tours, Marines say that they grew up with the show. That told me it had been a while.”

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Resurrecting old characters doesn’t always work, as Fox has seen recently with the lousy ratings for its “Get Smart” revival.

“It’s getting the elements in place the way the audience remembers them,” says Chas. Floyd Johnson, one of the “Rockford Files” executive producers. “Familiarity helps. But if it is just an excuse for bringing the characters back, and there’s not a good plot, it’s not going to be as interesting.”

The “Mad About You” producers have been careful not to tamper too much with the past. They would like to have Audrey Meadows on as Alice Kramden from “The Honeymooners,” for example, but fear that it “would be too sad” because Ralph was not around, said executive producer Jacobson.

On the Alan Brady episode, Rob and Laura Petrie are not even mentioned. Instead, the writers worked with Reiner to get Brady’s arrogance down just right.

And don’t worry, they didn’t forget one of Brady’s catch phrases:

“Shut up, Maurice,” he shouts to a maitre d’. Says Reiner: “I had to get one of them in.”

* “Mad About You” airs at 8 tonight, “The Fresh Prince of Bel-Air” airs at 8 p.m. Monday, and “Frasier” airs at 9 p.m. Tuesday, all on NBC (Channels 4, 36 and 39). “Simon & Simon: In Trouble Again” airs Feb. 23 at 8 p.m. on CBS (Channels 2 and 8).