WHEN the erotic lesbian magazine On Our Backs filed for bankruptcy in May, Susie Bright could not help but feel a sense of loss. Not only because, as the first editor of the magazine, she had put six years of time and effort into it before leaving in 1991, Ms. Bright said recently, but because, to her, On Our Backs symbolized a rebellious assertion of female sexuality that she sees as lacking in today's lesbian publications.

''On Our Backs was very defiant, saying, 'We're queer and we're sexual,' '' she said. ''I don't get the political hit from the current spate of lesbian magazines that I did from On Our Backs. You don't have that kind of revolutionary vision of, 'My God, we're changing the world.' ''

On Our Backs has been given a second life: in October, it was bought by HAF Enterprises, which also publishes Girlfriends, a two-and-a-half- year-old lesbian magazine published every other month in San Francisco. Heather Findlay, the editor in chief of Girlfriends, said she and her mother -- Erin Findlay, the publisher of Girlfriends -- expect to resume publication of On Our Backs in 1998.

Although more established gay publications like Out and The Advocate are aimed at both men and women, the readers of these magazines remain largely male. Indeed, most gay publications are still geared to a gay male audience. As a result, it is still relatively new for lesbians to have magazines of their own. ''Because lesbians have been underserved in the national gay press, women have not known to even look for themselves in those magazines,'' Sarah Petit, the editor in chief of Out magazine, said. ''There is a whole market of women out there who have the same niche potential that these gay men do.''