At NPR headquarters, executives are trying to craft content that will appeal to younger audiences. (Evy Mages/FOR THE WASHINGTON POST)

As NPR came of age in the 1980s, its audience matured with it. Three decades later, that is starting to look like a problem.

Many of the listeners who grew up with NPR are now reaching retirement age, leaving NPR with a challenge: How can it attract younger and middle-aged audiences — whose numbers are shrinking — to replace them?

NPR’s research shows a growing gulf in who is listening to the likes of “Morning Edition” and “All Things Considered,” the daily news programs that have propelled public radio for more than 30 years. Morning listening has dropped 11 percent overall since 2010, according to Nielsen research that NPR has made public; afternoon listening is down 6 percent over the same period.

Perhaps more troubling are the broader demographic trends. NPR’s signal has gradually been fading among the young. Listening among “Morning Edition’s” audience, for example, has declined 20 percent among people under 55 in the past five years. Listening for “All Things Considered” has dropped about 25 percent among those in the 45-to-54 segment.

The growth market? People over 65, who were increasing in both the morning and afternoon hours.

The graying of NPR, and the declines overall, are potentially perilous to the public radio ecosystem. NPR, based in Washington, serves programs to nearly 900 “member” stations, which rely in large part on financial contributions from their listeners. The stations, in turn, kick back some of their pledge-drive dollars to NPR to license such programs as “Car Talk,” “Fresh Air” and “Morning Edition” (federal tax dollars supply only a small part of stations’ annual budgets, and virtually none of NPR’s).

But as audiences drift to newer on-demand audio sources such as podcasts and streaming, the bonds with local stations — and the contributions that come with them — may be fraying.

“It’s a problem, and no one has really figured out what to do about it,” said Jeff Hansen, the program director at Seattle public station KUOW (94.9 FM). He noted that public radio was invented by people in their 20s in the 1970s, largely at stations funded by colleges and universities. “What they didn’t realize at the time was that what they were inventing was programming for people like themselves — baby boomers with college degrees.”

That audience has largely stayed loyal. The median age of public radio listeners has roughly tracked the median age of baby boomers. The median NPR listener was 45 years old in 1995; now he or she is 54, according to Tom Thomas, co-chief executive of the Station Resource Group, a public-radio strategy and research consortium. “The [aging] trend has been gentle and continuous for the last 20 years,” he said.

To shore up its appeal to a younger crowd, NPR’s contemporary managers say that they are going where younger ears are, both via digital technology and with programming that has younger people in mind. Although radio is still, by far, the dominant way to listen, NPR’s distribution chain now includes podcasts, Web text and streams, satellite broadcasting and social media.

Among its news initiatives, NPR in October and early November launched a series on the lives of 15-year-old girls around the world; it played on all of NPR’s news shows and on NPR also has attempted to foster a community of younger listeners through “Generation Listen,” a Web site that features audio and text stories, as well as news of community events hosted by young NPR listeners.

In more subtle changes, NPR added two new, younger hosts — Ari Shapiro and Kelly McEvers — to “All Things Considered” this summer, joining 68-year-old Robert Siegel. And it promoted Michel Martin, an African American woman who is the former host of “Tell Me More” (canceled last year) and now hosts “Weekend All Things Considered.” Editorial Director Michael Oreskes said the anchor reset is “an invitation to both traditional listeners and new ones to think about the programs in new ways.”

Some of the other brand-name talent at NPR illustrates the situation: Talk-show host Diane Rehm is 79; senior national correspondent Linda Wertheimer is 72; legal affairs correspondent Nina Totenberg is 71, and “Weekend Edition Saturday” host Scott Simon is a relative youngster at 63.

Last year, the organization launched a mobile app, NPR One, that streams both national and local public-radio stories via smartphones and tablets. NPR said downloads of the app have been growing, but it hasn’t released figures (notably, “Serial” — the massively popular and critically praised podcast — was produced not by NPR but by an independent public-radio organization, Chicago Public Media’s “This American Life”).

“If someone has decided that their phone is a better way to get information than their radio, we’re not going to change their mind,” said Oreskes, a former New York Times and Associated Press editor. “So our goal is to be there for them, wherever they are.”

Overall, audiences are growing on digital devices, said Emma Carrasco, NPR’s senior vice president for audience development. She estimated that 32 million people per week, about 1 in 10 people in the nation, hear or read (via something NPR has produced.

But it is unclear whether digital sources can fully replace the declining broadcast radio audience. No one knows, for example, how many people actually listen to the podcasts they download, or whether podcasts — still a small share of all listening — are a passing fad or an enduring format.

What’s more, NPR has to strike a sometimes awkward balance with its digital forays. By sending its programs directly to listeners via digital means, it risks bypassing and even competing with the stations that broadcast those shows — and supply the dollars that enable NPR to produce them in the first place.

“If I love [an NPR program] and I happen to be in the car, I may send money to my local station to thank them for the content,” says Larry Rosin, president of Edison Research, which analyzes audience data. “If I listen to the same program [via non-broadcast sources], who do I give money to? It does tend to break the logical chain” of contributions. “That’s what happens when an industry is disrupted.”

NPR has shown that it can move the needle on its franchise programs. A sustained promotional campaign paid off with a modest 2 percent gain in the audience for “Morning Edition” during the first six months of this year, Carrasco said.

The bad news, however, is that the radio part of public radio may be in slow and irreversible decline, a fate faced by newspapers, TV stations and other kinds of “legacy” media in the digital age.

To see this happening, people at NPR’s headquarters on North Capitol Street NW need look no further than across town to WAMU (88.5 FM), the public station operated by American University.

The station, perpetually one of the strongest in the public radio system, has been gradually cutting back after running in the red for the past three years. In fiscal 2015, ended in April, the station’s annual operating deficit was $2.58 million, a 52 percent increase over 2014 and more than twice that of 2013.

WAMU has experienced an 11 percent decrease in listening among its crucial morning-drive audience and a 9 percent decline during afternoon hours over the past three years, according to internal figures.

In January, the station laid off two full-time staffers and four part-timers, including Mary Cliff, who hosted a weekly folk and bluegrass music program called “Traditions.” It also dropped a locally produced Saturday program called “Animal House.” The station cut the frequency of its traffic reports last year, and dropped them altogether earlier this month, along with veteran traffic reporter Jerry Edwards. Familiar news voices Elliott Francis and Meymo Lyons left the station in recent months as well.

“As long as people are in their cars, they’re still going to want the sense of community and local connection” that radio provides, said Lettie Holman, WAMU’s program director. “But we have to be realistic about the fact that, overall, people are listening to the radio less and less. That does beg the question of what the sustainability is for the entire public radio system. We have to find diverse revenue streams. We have to find alternative revenue streams.”