Debbie Allen gets up from the table at a midtown restaurant. ''It's the finger tips on the hat, the shoulders that move, one and then the other - this is Fosse and Gwen working together,'' she says.
Miss Allen is describing the dance movements she learned for ''Sweet Charity'' - the demanding dance routines for which she was coached by Gwen Verdon, the original star of Bob Fosse's hit of 20 years ago. Miss Allen's portrayal of Charity, a woman of the streets, opened recently on Broadway at the Minskoff Theater, and both she and Mr. Fosse's revival have received critical praise and have been nominated for Tony Awards.
Miss Verdon coached Miss Allen in a Los Angeles studio for a West Coast run of the show about a year ago, sharing a theatrical tradition with other dancers who have coached proteges in their previous roles. ''Dancing with Gwen is like playing a duet with Miles Davis,'' Miss Allen said. ''It's an artistic high.''
Miss Verdon has similar views about Miss Allen. ''Debbie learns so fast and catches on to the essence of the scene so fast,'' Miss Verdon said in a telephone interview. ''I knew it was Debbie's role the minute we started working together.'' 'A Kind of Feistiness'
She said she remembered fondly the time during rehearsals when Miss Allen, who didn't know how to pop open a flattened opera hat, learned the technique. In the show, during a scene in which Charity sings ''If My Friends Could See Me Now,'' the actor with whom Charity is having a date gives her the opera hat. Charity doesn't know what it is, or how to open it. The actor shows her, and then she proceeds to use her fingers to open it, then closes it under her arm and giggles. She pops it on her rear, and it opens, then closes it between her knees.
''What thrills me the most was that she caught the idea at once of the fun and the game of how many ways you can pop open a hat,'' Miss Verdon said. ''Some people just dance and do everything technically correct. She had great fun doing it.''
Mr. Fosse agreed. Several people were being considered for the role, he said, when he asked Miss Allen, who was appearing with him in a benefit in New York, to read the script.
''Not many ladies can play that part because it requires singing, dancing and acting,'' he said, also in a telephone interview. ''The thing she has that I thought would be good in the part is a kind of feistiness, street toughness that seemed right for the part. Plus, she is a superb dancer and singer.''
During the rehearsals in Los Angeles, Miss Verdon shared stage pointers and offered the advice of someone who had been there before.
''Gwen is real tough, but she's tough with a soft edge,'' Miss Allen said. ''I'm in every scene but two, and she would remind me that the show was all night long. She told me where I could rest in numbers, like the scene after I had been to see the famous actor and had come back to the dance hall. Charity is upstage sitting on a box changing her dress and shoes. She has to be getting ready - rested - to do the 'Something Better Than This' number. Gwen said this is a good place to sit down rather than being busy in the locker. There are only a couple of places where I could do that, and I better take advantage of them.''
''Gwen is so giving,'' Miss Allen said. ''And she gives you space. Never did she give a line to me and say, 'Say it like this.' ''
She said the role of Charity Hope Valentine was her most difficult, especially because of Mr. Fosse's angular dance movements, in which the dancers dart like frightened goldfish and then glide into fluidity. Dancing From Memory
There are no dance notations for ''Sweet Charity,'' or for most dances in the musical theater. What remains exists mostly in the memories of the performers and in a few films. Miss Verdon, who used to be married to Mr. Fosse, said that when he decided to revive the musical, she had only agreed to help him find former dancers who remembered it. She soon discovered that she remembered the dances better than anyone else. Miss Verdon and her assistants taught the dance routines, and Mr. Fosse directed the scenes in Los Angeles.
''I do have memories about the show now that I see it with Debbie doing it,'' said Miss Verdon. ''I don't have to remember it anymore because it is there. It's terrific for me to see the show because I never saw it and never knew how I looked doing it.''
''Debbie is doing everything I ever did,'' Miss Verdon said. ''The only thing that might look different is that the movement on me may have looked more balletic: it looks more athletic on Debbie, but that may be because she's younger than I was when I did it.''
Miss Allen, who is 35 years old, has appeared in the movie ''Ragtime,'' on stage in ''Raisin,'' ''Anna Lucasta'' and the revival of ''West Side Story,'' and in ''3 Girls 3'' and ''Fame'' on television.
Sitting back in her chair in the restaurant, her face framed by frosted hair swept up in a bun in the back and by bangs in curly confusion, she smiled as she remembered one time recently when the tables were turned - when the student coached the coach. It was a short while ago when Miss Verdon was a guest star on an episode of the television series ''Fame,'' which Miss Allen - in addition to her starring role - choreographed, directed and co-produced.
''I was trying to explain to Gwen the concept for the dance in the scene,'' Miss Allen recalled, ''and she said, 'Honey, just tell me what you want me to do.' ''