Whenever jazz musicians are passing through town, they're likely to phone Felix Grant for some lighthearted conversation.

When bassist Billy Taylor Jr. died recently, one of the first calls about his death went to Grant - and his thousands of listeners got the news.

Step into a taxi cab after 8 p.m. of any week night and you're likely to hear the smooth baritone of Grant booming from the radio.

In the WMAL studios on Jenifer Street in upper Northwest near Friendship Heights, Grant sits in a swivel chair behind a white formica desk. Directly across from him, behind a glass panel, sits engineer Lorraine Wilcox, one of several people who plays the records and commercials heard on the show.

She's perched on a stool in front of a console with a battery of knobs and buttons.

"I like not having to play records or cue up commercials," Grant says. "Some guys at other stations have to do it all themselves. This way I'm going to say."

Felix Grant is the dean of Washington jazz announcers. He's been on the air in the same time slot longer than any other radio announcer in the country - 24 years. He also commands the top radio ratings for the 8 p.m. to midnight time period, according to Arbitron surveys, making him the No. 1 radio - AM or FM - personality in Washington in the evening hours.

Although he was criticized by some for mixing his programming with jazz and pop, Grant is still basically a jazz announcer. No radio personality playing jazz records has lasted as long.

His secret of commercial success is not elusive. He simply plays a variety of music - pop, blues, reggae, Brazilian as well as jazz - to reach a broad cross section of people.

Grant appeals to businessmen and bankers, students and street cleaners by playing the contemporary sounds of George Benson and the Brecker Brothers as well as Bunny Berigan and Art Tatum.

And, as a result, his ratings soar. According to Arbitron about 18,000 persons, ages 12 and over, listen to Grant between 9 and 10 p.m., the peak listening hour for his show, "The Album Sound." Estimates also show that more than 180,000 different people listen to Grant's show a week. He reaches more adults in the evening than any other radio personality.

"You've got to hold on tenaciously to keep something like this going," says Grant. "You can't play a 10-minute piece everynight of the week. That just won't go. The audience expects a certain amount of mix - and I try to give it to them."

On the air, Grant is all business. There's no jive talk or hip slogans, no condescending spiel about the latest record the audience should hear.

In soothing and moderate tones, he might say, "Today is W. C. Handy's birthday. He was born on this day in 1873. He was the father of the blues. He wrote a lot of songs, but the most popular was 'St. Louis Blues.' I think recently it was running neck and neck with 'Star Dust' for being the most recorded song. Something like 1,000 records have been made of each tune.

We're going to hear the granddaddy of the blues, 'St Louis Blues,' as sung by Carrie Smith with the New York Jazz Repertory orchestra."

His delivery is polished. His manner is always careful, sometimes scholarly. He speaks spontaneously from his knowledge of Duke Ellington or Joao Gilberto, B. B. King or Chicago, occasionally recalling interviews with them.

Grant spends three or four hours a day at home among his 10,000 records and hundreds of books researching his program, according to his wife, June. He says he plays mostly new material and reads books and articles about the artists he programs.

People think I'm sitting behind the microphone reading from album notes," Grant exclaims. "That doesn't happen. I prepare for this show. Putting it together is the hard part. After that I just come in and do it."

Everything about his work is meticulous. Engineer Wilcox says she enjoys working with Grant because he brings in his play lists carefully typed out - even in half-hour groupings so that his shows are like planned concerts.

The care he takes in his work extends to his dress. The other night, while reading from notes and answering the phone, the 5-feet-8, 150-pound announcer was a picture of controlled energy. Wearing a navy blazer, gray slacks, blue shirt and rep striped tie, Grant sits almost motionless while speaking. He doesn't gesture. His facial expression is usually serious, though sometimes he'll joke with Wilcox on the intercom.

Grant exudes composure. He tells the story of a young sales manager who came to the station several years ago and turned up his nose at the idea of a jazz program in prime time - in competition with television and rock on radio.

"Well, he started looking at the listenership figures and started changing his mind," recalled the announcer. "When he left the station for another job, he came up to me, said, 'You know, you educated me. I had never heard any of that kind of music. I grew up listening to the Kingston Trio.'"

Martin Williams, director of the Smithsonian's jazz program, says, "The musical life of this city would be considerably poorer without Felix Grant. He's one of the few people who programs without looking at Billboard and Cash Box. He functions in a highly competitive field - on a commercial station."

Cabdrivers echo that point of view in their own way. "I like him because he plays my kind of music - the old stuff," said one. Another said, "He plays everything - jazz, blues, old, new. It's a nice way to spend the evening while working."

Not everyone thinks Grant is the greatest. He's criticized for not playing much jazz - and that he plays, some say, is acceptable only to large audiences - the music of Duke Ellington, Louis Armstrong, Coleman Hawkings, Ella Fitzgerald, Oscar Peterson, Dizzy Gillespie.

Almost no other announcer will speak for the record about why Grant is successful. Off the record, they'll say his programming is predictable, if WMAL was not a middle-of-the-road station and needed listeners, Grant wouldn't be on the air.

Grant, the only WMAL announcer who isn't told what to program because of the respect the executives have for his musical tastes and jcommercial success, will only say that he couldn't keep a show on the air by playing nothing but pure jazz.

He's been at it long enough to know the formula for success. Grant got into radio in Washington after being discharged from the Coast Guard Service in 1945. First, he worked for WWDC for 7 1/2 years (he and veteran jazz announcer Willis Conover, now with the Voice of America, were together). He later switched to WMAL and he's been there since.

Grant's interest in music began in New York, where he was born more than 50 years ago (he refuses to give his exact age). "I was a good dancer and I liked jazz."

He listened to a variety of music as a young man and still tries to transmit that in his program. The other night, for example, he played a reggae piece by Pluto Shirlington and immediately the phone rang with a call from a homesick Jamaican living in Washington.

"I get a lot of calls like that," says Grant. "People are always calling telling me about a Trinidadian festival, a Haitian festival. They all want to tell me how good their music is."

Grant is especially close to the music of Latin America and the West Indies. He was the first announcer in the U.S. to consistently program Brazilian music. Many people credit create the bossa nova craze of the mid-60s.

He was the among the first to program records by guitarists Earl Klugh and George Benson before they became popular.

"Anything I play I try to transmit my enthusiasm for - whether it's Ellington, Coleman Hawkins or Brazilian music," he says.

How long will Felix Grant go on in this day when jazz is being diluted constantly by record producers and the musicians themselves in the search for hits?

He says he doesn't know. "It takes a tremendous amount of work these days to do intuitive, off-beat programming in this day of Top 40 record shows. I'm pleased with the acceptance I've gotten and I'd like to keep it."