William (Smokey) Robinson must be writing jingles for the Fountain of Youth. Impossibly lean and trim, he looks younger and healthier than he did 10 years ago to the day when he retired (in Washington) from the Miracles, from the concert stage, from 15 years as a natural musical wonder and triple threat--singer, songwriter and producer. "I'm 42 . . . or 24," he laughs easily. "I know those two numbers are in there somewhere."

In 1975, Robinson got "tired of being tired," came back as a solo act and picked up where he had left off. "The grass was not as green on that side of the fence as I had thought it was from looking over the fence," he says. He brought his liquid elegance to Constitution Hall last night.

On a sunny afternoon, Smokey is relaxing in his motel suite. He's torn between soap-opera addiction and looking for a game of golf. Those activities are indicative of his dual roles as an entertainer who spends too much time on the road and as the young exec who knows the value of a sub-par performance. Since 1963, Smokey has been a vice president at Motown, the company that was built on Miracles. In those long-ago Detroit days, there were only 10 or 15 employes at Motown, and Smokey's job was simple: write songs, produce groups and sign new talent, all the while pursuing his own career with the Miracles.

Smokey did most of his scouting from the stage, listening to opening acts in a hundred cities. He tried to hear them with the same open ears with which Berry Gordy had heard the young Miracles, who had been turned down by several other companies. "His main concern was the songs. We sang all songs I had written while going to high school. I looked for talent, because I knew we had songs and that producers could create an image if the person had talent. My main concern was whether people could sing. Even stage presence was not that important because I knew whoever we signed had to go to artist development. At Motown, it was mandatory."

Artist development never tried to mess with Smokey's distinctive high tenor, which he admits was an improvement on his high-school voice. "There I used to sing second soprano in the choir. I never really thought about it much until we started making records and everybody thought I was a girl. That was kind of a psychological setback at first--especially since they still thought that after the first hit."

His own idols had all been high-voiced singers--Frankie Lymon, Clyde McPhatter, Jackie Wilson, Sam Cooke--and the sexual confusion bothered Smokey, especially because the original Miracles did include a woman, Claudette Rogers. When we went around making personal appearances, everybody thought she was going to be the lead singer," he recalls with mock wounded pride. The situation had a happy ending, of course: Claudette, who has been his sweetheart since they were both 12, became Mrs. Robinson. They have two children, Tamla (named after Smokey's label) and Berry William Borope Robinson. Borope? After Bobby Rogers, Ronnie White and Pete Moore, the other Miracles.

At Motown, Smokey had a hand in most everyone's career, most heavily with the Temptations ("my favorites") and the Marvellettes. Displaying an uncanny feel for everyday language, he constructed 3-minute epistles that made radio worth listening to. Robinson wrote hundreds of songs, some of which ("Tracks of My Tears," "My Guy" and "My Girl," "Shop Around," "Going to A Go Go," "The Way You Do the Things You Do" and "Ooo Baby Baby") have become milestones in America's communal memory. His own favorite? "What's my latest record? Whatever that is, that's my favorite at this point," he says mischievously.

Despite being one of the most successful producers in pop, Robinson stopped producing himself two years ago after teaming up with producer George Tobin, who had turned one of his songs, "More Love," into a No. 1 hit for Kim Carnes. Smokey sent them another song he felt was "better suited for a girl," Tobin convinced him to cut it himself, and "Being With You" became Smokey's biggest hit in years. "It gave me a rest, time to back off. But I'm still in there, working with my two nephews Keith and Darryl."

And there is the time on the road, the rekindling of memories made easier because Smokey has seldom strayed from the fields of love. "I guess at heart I'm a romanticist. I do write songs of love. I've found that love is everlasting, forever, always; love is never passe'. You can never look ahead and say there won't be love in the world. It's not like a dance or something political that's here today and gone tomorrow. Take 'I'm In the Mood for Love.' That probably came out at the same time as the charleston. The song is still going strong, it's been great all those years, making plenty of money for whoever wrote it. The charleston is dead, no one is talking about it."

And so he sings those silly love songs, the happy and the sad ones, the ones that sound as good as a memory. Concerts are one long request line, and Smokey insists he never tires of singing his own songbook. In the last few years, he's become a better singer, his tones richer, his dynamics more varied. "But I'm not necessarily a singer," he insists. "To me, I'm a feeler. I wrote 'Ooo Baby Baby' 20 years ago and I've sung it 10 trillion times, but I still feel it. I just hope in the year 2002, somebody wants to hear the songs I'm writing now."