HAVING a singing dog is quite a responsibility. You must update his repertoire from time to time, and explain to friends why he's not on Johnny Carson's show. Every time you go to the piano, you're expected to start with his favorite, Fats Waller's ''Alligator Crawl,'' even though you wanted to play Beethoven.
But the rewards are worth it. Duke's singing has provided after-dinner entertainment for guests, has delighted visiting children, and has been the reason for interviews in our local Illinois newspaper and a Florida magazine.
Duke is a mature, handsome wire-haired terrier, like Asta of the old ''Thin Man'' series. He has taffy-colored ears, a dark ''saddle'' over a predominantly white body, and a short stub of a tail. His bushy eyebrows are like George Bernard Shaw's, his brown eyes are intelligent, and he knows a few words like bone, biscuit, squirrel, and cat. He understands ''Go look out the window'' but does not understand ''Get off the couch,'' nor does he want to.
As our family of three grown boys is musical - one tickles the ivories, another strums the guitar, and the third plays drums - it's only natural that the combo should have a vocalist. And that's where Duke comes in, although not always in the same key.
Duke's vocal styling has variety. Sometimes it's a low, melodious crooning, as when he sings ''Memory'' from ''Cats.'' (I wouldn't dare tell him the name of the show. He'd run to the window, ready to do battle.) Other times he accompanies ''Fig Leaf Rag'' briefly, but then his voice fades out. To boogie-woogie, however, he settles into the pronounced rhythm with short, staccato yips which almost keep time.
For several years his talent remained hidden. Occasionally I'd play a Chopin etude or MacDowell's ''To a Wild Rose,'' with no apparent effect on the sleeping dog. But when Dan, our jazz pianist, unearthed my old Fats Waller book one day and beat out the stride bass to ''Alligator Crawl,'' Duke found his voice. He's been vocalizing ever since. His favorites are rhythm numbers like ''Pinetop's Boogie,'' a classic. I enjoy it, too, because I used to jitterbug to Tommy Dorsey's hit platter in the Big Band era.
Duke's advent into our family circle is worth mentioning, although I never dreamed I was adopting a canine Crosby. A friend of mine had reluctantly decided to return him to the animal shelter whence he came, because he was upsetting her quiet household. Her housekeeper, who took him home on weekends, had likewise given up. Duke had munched on her philodendron and sampled a chair leg, and the TV wire chewing was the last straw. I was asked to ride with my friend to the animal shelter and manage this bundle of mischief while she drove.
As I held his wriggling form, I felt great pity. He'd be a two-time loser at the shelter, and who else would want him? We were halfway there when I said, ''Turn around. I'll take him.''
That was eight years ago.
Duke and I take walks three times a day. We play tag around the dining-room table. When the boys come to visit, he is constantly entertained. And he doesn't have to chew my potted plants, because if he looks bored or restless I just go to the piano.
One night I learned more. I was giving a dinner party the next evening and had planned to show off Duke. It was about 9:30, and I settled him in his bed in one corner of the living room planning to retire myself. But I underestimated his vocabulary.
''Are you going to sing for the people tomorrow night?'' I said, making idle conversation. At the word ''sing,'' he jumped up and walked over to the piano, taking his place underneath and looking as expectant as a tenor, waiting for his accompanist to start. I had to go through his repertoire, plus his new piece, ''New York, New York,'' before we both went to bed.
Friends have often asked why I don't try to get Duke on Johnny Carson's show, but I don't think it would work. Once I took him to a local recording studio, but he was too distracted. Even though I played his favorites with gusto and the studio owner got down on his hands and knees and howled encouragingly, Duke just raced around the room ignoring us. There were too many electronic marvels to examine.
William Congreve wrote the famous lines, ''Music hath charms to soothe a savage breast,/ To soften rocks, or bend a knotted oak.'' It's wonderful to me that melody has not only soothed this doggy breast, it has awakened something in it. But kindness and patience and the security of a permanent home had to come first before Duke's response to music's charms found utterance.