"Its been seven fat years and seven lean years and now it could be that the fat years have begun again. I'm a believe is such things."

The speaker is sandy-haired Michael Steward, whose mini-musicians of four characters plus four musicians who mingle on stage with the actors has just had a rare burst of New York's critical applause. It's titled "I Love My Wife," and the thinking is that this may be one breakthrough answer to the high cost of our stage's favorite sport, musicals.

"I Love My Wife" bowed in at the Ethel Barrymore Theater on a Sunday night. The next day Steward's first novel, "Belle," was published by Mcamillan.

"The Monday reviews for the musical were just great," says Stewart, "but the book world apparently works differently. I've not had any published reviews yet but I did get one vocally that means the world to me.

"There was a phone voice which said: 'I'm Ruth Gordon,' and I wondered yo myself who's putting me on? She must have caught my thought because she said 'Yes, I am Ruth Gordon and I think "Belle" is swell and we ought to get together for a movie about those old gals on the French Riviera.' Of course I said 'you bet' and we're going to try."

The most recent musical dip in Stewart's career was the musical "Mack and Mabel," seen here at the Kennedy Center, which took up three years of his and composer Jerry Herman's lives before it finally collapsed in New York. Before that was a straight play, "Those That Play the Clowns." With Alfred Drake, stephen Joyce and Joan Greenwood, that lasted four performances. "You slink away and lick your wounds," sighs Stewart.

But before those, starting in 1960, Stewart wrote the books for four hits in a row, "Bye, Bye, Birdie," "Carnival," "Hello, Dolly!" and "George M!" All were of the large cast, multi-set variety that today's theatrical economics appear to be ending.

"Now," says Stewart, "adding to my fat years feeling is the revival the Houston Opera is mounting of 'Hello, Dolly!" with Carol Channing heading a larger cast than in the orginal. This will be one of Carol 's smashing tours. She's almost alone now in touring the big musicals. There also are plans for a major revival of 'Bye, Bye, Birdie.' What a cast we had: Dick Van Dyke, Chita Rivera, Paul Lynde, Jerry Doge, Susan Watson, Kay Medford and Dick Gautier, the first breakthrough for all of them. There are a lot of good parts to fill.

"Yes, I think I can put away my worry beads for a while."

Stewart is a "librettist," the writer who constructs the story which carries the songs and dances.

Constructs is used here advisedly for of Stewart's first four hits one was adapted from a movie (Helen Deutsch's "Carnival"), one from a play (Thornton Wilder's "The Matchmaker"), one from an entertainer's life (George M. Cohan's) and the first was an original, "Bye, Bye, Birdie."

"That was happened in a funny way. In 1950 I had the first of four revues in which I was only one of many contributors, 'Alive and Kicking.' In the next few years, 'Razzle Dazze' had only eight performances, 'Catch a Star' lasted 23 and 'The Littlest Revue' 32.

"So, by '59 I wasn't doing too well, and when Lillian Hellman offered me a job as her assistant on the London production of 'Candide' I wanted that job. Trouble was, I had to pay my own way to London to get it. Alan Padula had a score by Charles Strouse, the composer of 'Annie' and a book about a couple who owned a yacht. The book wouldn't do. Could I write a new one in two weeks? I said I could for a thousand dollars, a cashier's check paid in advance that afternoon. Alan gave it to me, I marched over to the Cunard Line, paid for a one-way on the Queen Mary, went home, holed up for 13 days, brought the script to Alan on my way to the pier. Months later I learned it was working."

"Adaptations aren't easy. I had to leave out characters and incidents from 'The Matchmaker,' but I claim credit for one idea I believe made 'Hello, Dolly!' work. I split Dolly's last act 'Matchmaker' speech, putting part of it early in Act I. Because you know she still loves her first husband, that lets you accept some of Dolly's pretty outrageous behaviour and the plot.

"'Mack and Mabel' is Jerry's best score and I'm still crushed by the show's failure. We've since done it with a contrasting production, not the huge, chilling movie set you saw at the Kennedy Center. One production I've seen, done by a high school, worked the way we dreamed because the innocence of the young performers was a contrast to the essentially stark story.

"No, I don't know what's to be done about the large-scale musicals. Their costs now approach the million-dollar level. To keep them running you need $100,000 a week at the box office. Paying production costs at such scales is almost impossible.

"'I Love My Wife' is from a farce I saw in Paris, 'Viens Chez Moi. J'habit Chezune Coquine' by Luis Rego. It hit me immediately as a possible musical and for the first time I did the lyrics. Cy Coleman's score sparkles. We opened very low key so the surprise element made the reviews even better.

"Now you see what I mean about seven fat years and seven lean years and, I hope, seven fat years?".