SAN FRANCISCO (AP) _ The Jefferson Airplane, whose soaring vocals and political lyrics helped define the psychedelic rock of San Francisco's flower power era, will fly again.

Grace Slick, Paul Kantner, Jorma Kaukonen and Jack Casady are planning to reunite for the first time in 17 years and are reportedly close to signing a recording contract.

Marty Balin, who left the group after the ''Volunteers'' album in 1969, hasn't come aboard yet, but Kantner is still hoping the singer will become part of the ''born-again Airplane.''

''I think we had all thought about reorganizing the Airplane in the last few years,' Kantner said after the reunion was announced Wednesday. He said the idea ''really came together'' after his own group played at the new Fillmore auditorium in March 1988.

''Grace came out to sing at that show and we all felt very good - Jorma and Jack seemed to like the idea of us all working together again, and we'd all written new songs and wanted to perform them,'' Kantner said.

Slick, whose powerful vocals made ''White Rabbit'' and ''Somebody To Love'' rock'n'roll classics, also sang with Kantner earlier in 1988 at San Francisco's Great American Music Hall.

The two once lived together and have a daughter, China.

The Airplane's albums included ''Surrealistic Pillow,'' ''After Bathing At Baxter's,'' ''Crown of Creation,'' ''Bless Its Pointed Little Head,'' ''Volunteers,'' ''Bark'' and ''Long John Silver.''

Casady and Kaukonen formed ''Hot Tuna,'' an acoustic blues band, in the early 1970s and eventually left the Airplane. Slick and Kantner worked on several projects together and formed the Jefferson Starship in 1974.

Kantner left the Jefferson Starship in 1984, and his departure led to a legal battle with Slick over money and use of the band's name. A settlement in 1987 gave the group the right to use the name Starship; Kantner got $250,000. Slick set out on a solo career early last year.

''Grace seems 'reborn' after leaving the Starship group - she's become involved in the World Wildlife Fund organization and one of her new songs is dedicated to pandas,'' Kantner said.

''The four of us - myself, Grace, Jorma and Jack - are planning to record, with Ron Nevison producing ... later this spring,'' he said. Nevison ''was on our road production crew years ago, and now he's a big record producer.''

''We haven't signed a contract, yet; and yes, RCA - our original label - is interested.''

''With the record finished and on the market by midsummer, we hope to go on tour, and we hope, along the way, that Marty will rejoin us,'' Kantner said. ''Marty has been involved in his own thing for quite a while and we don't know, now, how he feels about joining the born-again Airplane. He's very much his own man, you know.''

Kantner said each group member will probably have three songs on the new album. ''Mine will be poetical-political statements like 'Falling in Love with Nicaragua.'''

Slick said the reunion ''was loose, it wasn't planned.'' She said the reaction to last year's Fillmore show ''was more striking than we planned. So we thought we'd make a record.''