Townshend says "Floss" will focus on a pub-rock musician and his troubled relationship with his wife, who runs a riding stable.
He says he wants to use the angry medium of rock 'n' roll to take on issues of aging and mortality facing the baby boom generation.
Songs from "Floss" will feature on a new Who album due out next year,
Townshend says he is in talks with New York producers about staging the show in 2011.
Townshend's previous "rock operas" include "Quadrophenia" and "Tommy." Both started life as albums and later became films and stage musicals.