Miami radio listeners who want some extra confidence can tune in these days to AM 980 -- "Your Motivation Station."

Since August, it has been pumping out positive thinking 24 hours a day, 5,000 watts strong, in a fast-moving format that sounds like Top 40 without music. It gives tips on courtesy, caring and achieving excellence, and pep talks from motivation specialists. It airs health advice, news edited to stress the upbeat, and tales of products and people that weren't supposed to succeed but did. Features like "Energizer of the Day" and "the WNN Supercharger" round out the broadcast day.

In New York, another commercial AM station is on a new specialized track: round-the-clock sports. WFAN updates scores from games big and small every 15 minutes. It fills the airwaves with stadium hero interviews, trivia quizzes and three-minute features on subjects like sports surgery and workout routines.

In Los Angeles, meanwhile, AM station KMNY is trying something similar for the financially minded. This "Money Radio" is a 24-hour report on stocks, commodities, corporate strategies and the business world in general.

These are tough times for AM, the venerable pioneer of commercial broadcasting, and it is fighting back. With experimental formats like these and technical innovation to banish tinny sound and interference, it is working to stop a seemingly endless slide that has taken it to a 30 percent share of the listener market. As recently as 15 years ago, it had 70 percent of the market.

"What are we going to do to salvage the AM spectrum?" asked David E. Parnigoni, senior vice president-radio of the National Association of Broadcasters. "That's a real serious question."

What especially troubles AM radio is a generation gap among audiences. AM draws in older people, who tend to like news, information and "nostalgia" formats. FM has the younger audience, which likes music, music, and more music.

Now AM operators are wondering whether their listeners will be replaced when they die out. Will baby boomers gravitate toward AM as their hair goes gray?

"That generation has been raised on FM and FM music," said Wayne Vriesman, vice president of Tribune Broadcasting Co.'s radio group. "Many of them today hardly know that AM exists." He said he thinks that technical improvements will help but that they alone don't hold the key to a revival.

"AM," he said, "has to produce programming that is going to attract -- programming besides news and information and talk that's going to attract these younger people as they mature."

To be sure, AM is nowhere near extinction. About 4,900 of the close to 8,940 commercial radio stations in the United States are AM, doing a business estimated by Duncan's Radio Market Guide at $1.7 billion to $1.9 billion last year. FM is a far bigger business in dollar terms, though the station numbers are lower. In 1987, the 4,040 or so stations rang up at between $4.8 billion and $5 billion in sales, Duncan's estimates.

As earlier as the 1940s, some industry sages predicted FM's dominance. Its range might be shorter than AM's, but its tone was deeper, richer, making music more true to life.

The changeover gained speed in the late 1960s and early '70s as low-budget, underdog FM tried new formats in "beautiful music" and rock. "There was new programming that attracted people as well as superior sound quality," said James Duncan Jr., editor and publisher of Duncan's Market Guide.

FM's sparser advertising helped, too. At first, that was because hardly anyone wanted to buy time on FM stations. Today, there is plenty of interest, but FM still airs fewer ads because the industry believes that listeners of all-music formats won't accept the volume of ads that air on AM. Eighteen minutes per hour of advertising is common on big-time AM; FM typically has about half that.

AM's decline may have been speeded by the falling quality of its own sound. Despite the mass defection of listeners, AM stations have continued to proliferate, crowding the spectrum and causing static on stations adjacent on the dial. At night, when the upper atmosphere bounces AM signals back to earth, the stations' range increases, making the noise even worse.

Today AM has retreated to a large degree into talk and information, in part on the logic that the human voice doesn't sound that much better on FM.

There is still good money to be made in formats like that of the Washington area's lead AM station, WMAL -- news, traffic reports, community service, personality disc jockeys, even a bit of music. In many big cities, the biggest revenue station is still AM -- WMAL here, WGN in Chicago, WINS in New York.

And in rural America, general-interest AM continues to thrives. Technical capabilities explain much of that: FM rarely carries more than 65 miles, making it commercially impractical in areas of low population density. A strong AM station (50,000 watts is the maximum allowed) will extend 750 miles or more at night and not be blocked by hills and valleys the way FM is. (AM continues to do unusually well in the hilly San Francisco area, partly for this reason.)

But for most smaller AM operators the squeeze continues, and a feverish hunt is under way for specialty formats. If listeners want something and your station alone has it, they'll tune to you whether you are AM or FM, the logic goes.

"They don't really have to have that mass appeal in order to stay in business," suggested Jim Gallant, director of broadcast operations at WMAL-AM.

Thus it is that in a suburb of Little Rock, Ark., a children's station has been on the air for the past 2 1/2 years. KPAL (K-Pal) is on the air from 6 a.m. to 10 p.m.

"The only reason we don't go longer is our age group goes to bed," said the station's general manager, Bill Henslee. Advertising is often aimed at parents who listen in -- both by choice and necessity.

Other specialty formats don't make the cut, however. Station WHRS in Winchester, Ky., the heart of racing country, adopted an all-horse format recently. But it dropped it for "beautiful music" after the local station filling that more lucrative niche got out of the business.

About the only music category in which AM remains king in urban areas is "nostalgia." Big band music, introduced to America in the 1930s by way of vacuum tube AM, sounds more authentic to many older listeners on that medium. So do many rock 'n roll hits of the '50s.

Station KRVN of Lexington, Neb., has found success through both rural service and one of the country's older specialty formats. It opened in 1951 as an all-agriculture station and today, at 50,000 watts, brings news and views on that subject to farm kitchens and tractor cabs across a large swath of the Midwest. It will go 24 hours in March.

AM hoped to brush off the cobwebs a bit with the unveiling of AM stereo in 1982, years after FM had adopted stereo. The trouble was that not one but five systems, all incompatible, went on the market that year. The Reagan administration had just come into office and deregulation was its theme. The Federal Communications Commission declined to set a single standard for stereo, saying market forces would do the job better.

"It was a disaster," said Tribune Broadcasting's Vriesman. "We lost years through that process." Radio manufacturers, consumers and stations postponed big-ticket equipment investments until it became clear which system would win out. Their dithering, of course, slowed the weeding-out process.

Today, only two systems remain, made by Motorola Inc. and Kahn Communications Inc. Nonetheless, only about 10 percent of the country's AM stations broadcast in stereo, although that number may increase.

The number of stereo receivers is slowly growing. Auto makers are starting to install them in new models, radios capable of tuning in either system have appeared, and industry officials are putting their heads together to work for a single, voluntary standard.

The industry has been busy crafting other technical improvements, too. Surprisingly, it had worked for decades with no standard for certain characteristics of the AM signal. As a result, receiver manufacturers could never tell how best to design their equipment to match what would be coming from stations, and vice versa.

But in January 1987, after lengthy negotiations, it settled on a voluntary standard. About 600 stations are broadcasting in it now, and equipment manufacturers are starting to incorporate it in their product lines.

Another project, sponsored by the National Association of Broadcasters, is intended to redesign AM broadcast antennas to extend their range and reduce interference. An experimental antenna is soon to be built on the Beltsville campus of Howard University, according to Michael Rau, the association's vice president for science and technology.

The FCC, meanwhile, is in the midst of a lengthy inquiry into the methods it uses to assign broadcast frequencies. Many of the criteria were established decades ago when the industry and equipment in use bore little resemblance to today's. Those criteria could be hampering AM's ability to compete in the radio marketplace, the commission acknowledges.

At the same time, the FCC is getting ready to expand the AM band to bring it in line with new international allocations. It now lies between 540 and 1605 kilohertz. It will grow to 1705, effective probably in 1990.

For station assignments, the FCC is considering creating what would amount to mininational networks, with one operator getting rights to operate on the same frequency in different parts of the country.

Despite AM's troubles, there will no doubt be applicants for that new band space. There are always people trying to get into the business. The operator who goes broke is still generally able to find a buyer with an idea of how to keep the station on the air.

But not always. At any given time at least a couple of hundred stations are silent, said Duncan. He predicted that closures are going to become more common in the not-too-distant future.

For years WBIG of Greensboro, N.C., lost money with a succession of formats. Finally, the owners decided that the land on which the station stood would be better used for commercial development.

Attempts to move the station or sell its license did not succeed, so the equipment was wheeled out and the license turned back to the FCC. Said George Grills, a vice president at the station's parent company, Jefferson-Pilot Communications Co., "We elected simply to go dark."