Already by the mid-1970s, Casey Kasem and his “American Top 40” radio show felt like an anachronism, a hokey blast from a time when everything was supposedly hunky-dory, when all the kids danced to the same tunes and America was all about possibility.

Kasem’s weekly countdown of the top hits arrived at the radio station where I worked not through the modern miracle of the premium-quality electronic network feed from New York but in the regular mail, in boxes holding four 12-inch vinyl records containing all the music, Kasem’s corn-pone storytelling and the national ads. All we had to do was pop in the local ads.

It was backward, old-fashioned, impossibly uncool. Every DJ in the land rolled his eyes at the persistent popularity of Casey’s countdown, his long-distance dedications, his tear-jerking tales of men in uniform sending their love and a song to their girl back home. And every station manager who could land the rights to “AT40” held on for dear life, because although the jocks made fun, the listeners were totally addicted.

This was the era of FM’s ascent — in 1980, FM listening topped AM radio for the first time — the beginning of radical new formats such as progressive rock- and singer-songwriter-focused stations, the start of the splintering of the American media and of popular culture, the birth of the niche. Radio was all about the new science of psychographics, the idea being that there would be a different station for each demographic group, a division of tastes and cultural experience depending on your income, age, location and race.

And then, once a week, on Sunday morning after church in every town across the nation, in the midst of all that fine-tuning of formats, Americans came together again, as radio stations played Casey Kasem and the “hits from coast to coast.”

Casey Kasem, host of the "American Top 40" radio show. (James A. Parcell/The Washington Post)

The accidental genius of Top 40 radio from its inception in the late 1950s had been to tap into America’s exploding youth market at a time when businesses had not figured out the transforming nature of the baby boom. By the ’70s, when Kasem, who died Sunday at age 82, started his show, the mass appeal of Top 40 was being sliced and diced into demographically targeted formats. That left the field wide open for Kasem to bring us all together again, if only for three hours each Sunday.

He was a cute, bubbly, energetic voice, benign, anodyne, like Dick Clark before him and Ryan Seacrest later. Kasem had none of Johnny Carson’s bite, hardly any of the sex appeal of the pop heartthrobs whose tunes he spun. He was steady and unthreatening, like Walter Cronkite or Ed Sullivan, the other men who earned the nation’s trust mainly for being there, dependable and uncontroversial.

He was a Lebanese American from Detroit who spent his time in the Army spinning records on Armed Forces Radio, a little guy blessed with a captivating voice that made him sound forever young yet authoritative and fun. He was for many years the voice of Shaggy on the “Scooby-Doo” cartoons, and for a few years in the late-’70s, he was the voice of NBC television.

But it was during those Sunday visits, when Americans were driving home from church or getting the groggy of Saturday night out of their systems, that Kasem found his way into what was then still one big audience. On a single Sunday in 1977, Kasem played Glen Campbell’s “Southern Nights,” The Spinners’ “Rubber Band Man,” Rod Stewart’s “Tonight’s the Night,” Bill Conte’s “Theme from Rocky,” Electric Light Orchestra’s “Telephone Line” and KC and the Sunshine Band’s “I’m Your Boogie Man.” An impossible mash-up of tastes and subcultures, yet there they were, selected not by psychographic research aimed at molding a demographically pure audience but by the old-fashioned method: counting record sales and playing whatever people were buying.

At a time when the questions that could place a stranger were shifting from “Who’s your favorite DJ?” or “What’s your favorite song?” to “What’s your station?” Kasem created a refuge for those who still wanted to know what the other kids were listening to.

The era when a single Top 40 station — great radio stations like WPGC in Washington, WABC in New York or WLS in Chicago — could dominate a market, drawing 30 or 40 percent of listeners, was over. Now, niche stations were happily profitable with 5 or 6 percent slices of the audience.

Kasem counted down the 40 best-selling hits every week from 1970 to 2004 (for a few years in the early-’90s, he lost control of “American Top 40” and marketed his own show as “Casey’s Top 40”), with more than 1,000 stations carrying his program during its best years.

As far as listeners could divine, Kasem was format-agnostic. He seemed to like everything, from syrupy pop to hard rock to country to disco. What linked those varieties of pop music were the stories behind them, the mini-biographies that Kasem had started inserting into his shows on KRLA in Pasadena, Calif., in 1963, quick bits such as, “In a moment, we’ll hear a song by a former truck driver who parlayed an accident into a million bucks.”

Kasem’s show resisted the splintering of the culture until rap came along; starting in the early ’90s, the stations that aired “AT40” would no longer tolerate Kasem’s openness to whatever tunes made Billboard’s sales charts. To accommodate his stations’ belief that their listeners would not accept hip-hop mixed in with Celine Dion and Trisha Yearwood, Kasem switched from Billboard’s list to one based on airplay at the nation’s top-rated radio stations. That allowed an occasional Will Smith or Sir Mix-A-Lot number onto Kasem’s countdown, but it kept most hip-hop off the show.

But Kasem’s anything-goes approach had been in trouble long before that. In 1979, a Cleveland station pulled “AT40” from the air on one Sunday at the height of the disco craze, replacing the program with a disco-free top 40 that mimicked Kasem’s style but gave listeners only the songs that station managers thought they would tolerate.

There was no keeping the old coalition together. Whether it was chicken or egg — whether radio was merely adapting to increasingly segmented listener tastes or was, rather, leading listeners away from variety to satisfy advertisers who wanted to reach specific demographic groups — Kasem’s approach was, by the mid-’90s, widely dismissed as archaic.

The show continued and even won new audiences when the archival countdowns from the ’70s and ’80s started airing on XM satellite radio in 2006, but the promise of Top 40 — the idea that if you’d just wait a few minutes, you’d hear the song you loved, and along the way you might discover something you hadn’t known you’d like — was spent, lost to the new on-demand culture.

From Three Dog Night’s “Momma Told Me Not to Come,” the No. 1 hit on “AT40’s” first show, to Outkast’s “Hey Ya!,” the No. 1 on Kasem’s final “AT40,” the show was a weekly reminder of what Americans had in common — not just big ideas like liberty and democracy, but small things, single voices that remind us of who we are and what we care about. No romance was too saccharine to become the stuff of Kasem’s long-distance dedications; no adolescent’s attachment to a silly love song was ever to be poked fun at.

“Keep your feet on the ground and keep reaching for the stars,” Kasem instructed us at the end of every show. Hokey, cliched, all that, yes, but he produced a little catch in the throat every time, and that optimism, that sense of community, is what kept people coming back. It’s also what kept them, at some level, together.