FELIX GRANT has had laryngitis. Really. He's been out most of this week, and it bothers him that people might think he's avoiding them - dodging publicity or something. He's not, he says. He frankly doesn't like to miss a night.

As of Sept 1, he will be missing five a week.

They are Monday through Friday - where the 58-year-old Grant for the past 25 years has been spinning jazz records on "The Album Sound," 8 to midnight of WMAL, 63 on the AM dial. Now he'll be doing weekends only. And this also bothers him, though it's not quite as easy to talk about as laryngitis and the love of one's work.

He'll talk about the schedule change reluctantly. "It was a great surprise. People say it shouldn't come as a surprise. Well, it is.

"I am not pleased," he says when the point is pressed. He glances out the window of the plush, white-carpeted living room in the Southwest Waterfront condominium he shares with his wife June, two tiny terriers named Fawn and Felicity and about 10,000 mint-condition albums. It's the impending curtailment of jazz on the radio that really seems to bug him:

"I don't want to leave the impression of being elitist, above reproach, I-know-better-than-anyone...but my concern is for the whole jazz area, that's the thing that concerns me, because I've devoted a large part of my life to it. And, in a sense, I've had a ball."

In general, 25 years of work at one craft tends to develop some excellence. Grant is generally acknowledged to have taught more people more things about more types of jazz than just about anyone - and he does it with studious precision.

Some say, though, you can't be so excellent that you miss out on some important changes around you. For instance, no self-respecting blacksmith 100 years ago could have accepted the notion of a 500-pound wagon being moved without a horse in front of it. Imagine how a modern-day jazzsmith feels about a pulsating 500-pound mass of sequins, sex appeal and salability by the name of Sister Sledge being moved with neither a decent tenor solo nor more than three major chords in front of it.

After a lifetime of listening - more than half of it daily and professional - Grant's ears are probably among the most experienced in the business. And they complement a ruddy, thoughtful face and a relaxed baritone voice that at the moment is speaking of the work that goes into each nightly show: three to five hours each day of auditioning, researching, checking facts, and more auditioning.

"The hard part," he says, "the hard work is putting the show together. Doing it, going out to the station, as I've said many times, is just doing it."

He has probably heard - and judged for his listeners - more music than most of the jazz musicians with whom Grant is friendly. (And that's most of them, both here and in Latin America, where Brazilian and reggae music have held a special interest for Grant since he discovered them about 10 years ago.)

And the use of judgment, Grant says, comprises much of the job's challenge: "When I get a record, I've got to make up my mind about the record that day - I can't wait for Billboard or Downbeat - I've got to almost lead the way, in one respect, and go on record as saying, for example, "This is one helluva performance."

"It may sound presumptuous of me, but as a professional you've got to take those kind of stands."

Which brings him to what is affectionately known as pop music, where Grant says they don't ask for much. And consequently don't get it.

"I wonder what would happen to radio stations that play pop music if for some reason they had to do without Billboard for, say, three months. They wouldn't know what to play. They don't make these kinds of decisions - someone has to tell them, by way of a bullet or something.

"There'd be chaos. Among the bulk of pop radio stations, the same music is being played in Seattle, Wash., as in Key West, Fla. - the exact same records ! And if they didn't know what to play, what would they play? They'd have to use some imagination. I don't think they have it."

Grant would much rather talk about the jazz (and its players) that he's come to know in the years of playing it on the radio every night. He's got lots of stories. More than he could ever tell on the air - because on the air, he says, the most important thing is the music (though he's always ready with a salient fact or two about an artist or selection). "There's never been any hype, there's never been any con - that sort of thing. It's been straight - and I've felt that the music had to carry itself."

Oddly enough, that's pretty much the reason he won't be doing it as much anymore.

WMAL's management decided last week that the future of AM radio - in a town where 67 percent of the listeners are now said to be tuend to FM - does not lie so much in music as it does in talk, and they mean to replace Grant with veteran talker Johnny Holliday, an experienced entertainer who'll do interviews, comedy, call-in s and a little music. On his new shift, Grant will take the "braoder base" he says he was asked to work into his show five years ago and fairly throw it out the window. He'll do a 9-to-1 "strictly jazz, innovative, often live" show Saturday and Sunday nights.

The move, says operations-program director Jim Gallant, was made with an eye on the future. A eye on the past had already told them that Grant's "Album Sound," the No. 1 show at night for close to 15 of its 25 years, had begun to lose listeners about a year and a half ago, while others - all of them FM, most noticeably black album WHUR and WOOK, and top-40 WPGC - began to gain.

The reasoning doesn't sit well with Grant, who thinks the drift toward FM may be the result of too much talking on AM. "Seems to me that if 67 percent of the people here are turning to FM, that must mean they want to hear music," Grant says. "So why drive them away from AM by not offering them any?"

Martin Williams, director of the Smithsonian's jazz and American cultures division, says Grant "has made an enormous contribution to music in Washington. He's one of the few people around who programs without the help of any top-40 charts and relies just on a really strong sense of quality and taste.

"It's just not good," Williams says, "to have a town where you've got the top-40 kids' sound on one end, and on the other end the Mozart-Kennedy Center type of music. You've got to have someone like Felix maintaining a status quo, a standard of excellence.

"There are whole generations of people in this town whose musical tastes, jazz and otherwise, were developed listening to Felix. That's the loss." CAPTION: Picture, "When I get a record, I've got to make up my mind that day...I can't wait for Billboard or Downbeat." By Roger Piantadosi - The Washington Post