Since the new paperback edition of Rita Mae Brown's funny, exuberant novel about growing up gay in America was published in September, orders for the first 250,000 copies have come so quickly that Bantam has already cranked out a second press run of 50,000 more.

The cover of the new version of the underground best-seller says: "Being Different Isn't Really So Different." No one needs to tell that to Rita Mae Brown. She's the one who wrote the line.

Four years ago Brown was a feisty 28-year-old feminist with a prankish sense of the ridiculous and a flair for flamboyance that sometimes got her into trouble with her friends. About all she had to her name were her movement credentials (she was an early member of NOW, a founder of the radcial feminist group. Redstockings, in New York and a member of the Washington lesbian collective, the Furies), a cat named Sweet Baby Jesus, a place she shared on Capitol Hill and a manuscript she had just completed.

And, in the public eve, a big, splashy scarlet letter "L" that stood for lesbian and didn't make it any easier to capitalize on her other assets.

So when Daughters, Inc., a women's publishing house struggling in late 1973 to get off the ground, published in its first batch of five novels "Rubyfruit Jungle." Brown thought she was lucky to walk away with $1,000 in cash and what would eventually add up to enough in royalties to pay the rent.

The book didn't seem to have much going for it. It was, after all, lesbian literature from an unknown press by a radical feminist/gay author who'd even gotten herself kicked out of NOW - and worse, to get a copy the odds were you'd have to scratch up the address of the publishing office somewhere in Vermont and write for it, because the telephone did not always work and the bookstores weren't stocking it yet.

About all you could say for "Rubyfruit Jungle" was that it was a slick piece of writing - an engaging sometimes vuigar, often moving account of growing up lesbian in the poor, rural South and heading for New York and the recognition that for the woman who turns her nose up at convention, home may be a hard place to find.

Told that she's illegitimate by her mother, shuttled with family and cousins from a small town in Pennsylvania to another in Florida. Brown's poor, decidedly uncouth young heroine, Molly Bolt, makes the most of her chances and cruising precariously among the gay-world stereotypes feminists have disavowed, somehow manages to remain her own woman.

She may have been too good to be believed, but Molly's reputation spread. By last February, when Bantam finished negotiating with Daughters to publish a mass-market version of "Rubyfruit," which left Brown and Daughters each $125,000 richer, the smaller press already had sold 70,000 copies of the book.

The new edition quickly reached second place on the Long Island Newsday paperback best-seller list, and film rights to "Rubyfruit Jungle" have been purchased by Iris Productions, with release scheduled for 1979. Brown is now on a PR tour touting the book.

So four years later it seems being different really isn't so different any more - or at least it's no longer taboo. More than 60 books with homosexual themes were published or are scheduled to be this year. In August, Publisher's Weekly reported that sales have increased and are expected to get even better with the deluge of new books.

In four years Rita Mae Brown has become "Older," she says matter-of-factly, but with an amused grimace. "I've grown older; we all have. You get the face you deserve," she drawls. "When I look at mine" - she breaks out in a grin - "it's still full of the devil."

That may be true. Those sudden funny flashes are still there - "Sweet Baby Jesus is going bald, and I have six or seven gray hairs myself," she quips, then rattles on about her new wealth.

She bought her mother a 1977 Dodge Aspen, for one thing. But Brown seems more thoughful, more tentative now as an insider looking out than she was an outsider looking in. She is preoccupied with survival, the meaning of it; and she is up to her ears in words.

She was written almost 1,000 pages since "Rubyfruit" and her two earlier poetry books, "The Hand That Cradles the Rock" and "Songs to a Handsome Women," were published, one novel. "In Her Time," that is already out, and another - a 500-page behemoth - ready for publication. There also is more poetry, movement papers, and two screen plays, one about a murder in a department store ("anybody who's been there will know it's Bloomingdale's"). The second - also in collaboration with writer Arnie Riesman, is the screenplay for "Rubyfruit."

"People have been asking for the film rights for years, but since I have an interest in film myself, I retained them with the idea that I might some day make the picture. Then I met Arnie and Ira Yerkes, and decided to let them do the film. Everything I wanted, they agreed to - that a woman had to direct, that I could do my own script, that Chris Williamson, whose music I really like, do the score."

Joan Tewksbury ("Nashville") was selected to direct and casting is to be completed soon. "We all agreed we'd like to see Molly played by an unknown, but we wanted some solid talent to back her. My fantasy? I'd like to see Andy Griffith play my father. Her kinda' reminds me of him." Brown's eyes open wide and take on a wicked glint: "I would have picked Marie Dressler for my mother - she was too fat. You'd better say she was too fat or my mother, who is not fat, and is quite pretty in fact, will have a fit. But she was a fabulous character, real and rooted - she'd make a wonderful Carrie."

Brown's mother, Julia, is in her 70s, and while her daughter's feelings about the woman who adopted her as an infant are complicated, the affection if fierce. "Mother didn't have anything, but she gave me a lot. What I got from her is - she taught me survival skills, like to watch what people do and not pay attentionto what they say. Survival means a lot to me; I've been hearing about it all my life. I'm constantly trying to refine the ways you can survive.

"Why, when I was adopted I was only three months, and my blood mother had dumped me in an orphanage because she couldn't manage. It was winter; times were hard. When Julia and Ralph (her father) heard about it, they were on the other side of Pennsylvania and Julia had pneumonia.

"But she got Ralph and her sister to come after me, and somehow they got me out. I was sickly; the doctor told them I was going to die anyway, so they should just leave me. But they borrowed gas coupons from all their friends and collected all the milk they could find, and brought me back to York in the middle of a blizzard. Where there was a light, they'd stop and ask to warm me up and warm some milk. I guess I owe a lot to the people of Pennsylvania. Without them. I might not be here."

The not-yet-published novel, "Six of One and Half a Dozen of the Other," sets aside feminist politics and lesbianism to celebrate the lives of Julia and Julia's older sister, who is past 75. "It's from 1905 to 1980: it's every thing I know, what I've heard, what I've made up. You get the whole enchilada." Brown jokes.

She describes the women, almost unconsciously falling back into a drawl; "Mother is a Lutheran, very organized, efficient. But she sees pretensions and she makes fun of them. Her sister was Catholic and a social climber - it's not easy to be a social climber when you are poor as that." They grow up in a little town split right down the middle by the Mason-Dixon line; in the novel, they live on the south side. In real life, Brown, to her often-voiced dismay, was born north of the line. That's poetic license.

In one passage, Julia is helping deliver some moonshine, and when her partner gets sick, she asks her sister to go along. "Of course some law-abiding citizen sees them, and they end up getting chased by federal agents and have to escape. The finally end up in the middle of the night in this old deserted meadow, all by themselves." There is only one small bottle of shine left, and Julia is so worn she opens it and takes a gulp. "Julia, don't drink in public," Louise says primly.

"I'd like to have lived in that world . . . but I'd have survived anywhere," Brown says. "It's the people who live against the odds - and particularly the ones with a sense of humor - who fascinate me." She counts among them Julius Ceasar and a number of generals whose stories she knows because her favorite reading is military history. She reads Gabriel Garcia Marquez, too and Bertha Harris (feminist lesbian author of "Lover"), but would prefer to curl up with the Battle of Leningrad to reading much else published now. "Philip Roth, that other stuff, I don't know what that's all about. It's so self-indulgent I just can't bear it, that whole white male trip."

Some of Rita Mae Brown's surviving these days is done in Cazenovia, N.Y., where she teaches at the Women's Writers Center. The other affiliations she maintains are with the National Gay Task Force and the advisory board for the National Women's Political Caucus. Cazenovia is cold - "I'm too little for long underwear, so I have to put on layers.

"I wear gloves with the fingertips cut out so I can hit the typewriter. Sometimes I even use a hot-water bottle." But Brown works. "Very hard; I don't have time to waste," she says. "I have a list next to my typewriter of all the books I want to write during the next ten years, with the titles already picked out. I try to write books that will stretch me. Most will be funny, or at least partly, and about people surviving, and sometimes triumphing."

Brown wants to work, and to live, in Charlottesville, Va. She wants to get land, to grow things. "Acres, lots. Put some of them in corps - space, green." She is intense as she talks about it.

She is looking for a buffer - "you take such a buffeting in political activities. I've been involved since 1968 and some of it has been intense. Now I'd like to take care of myself a little" - and have an opportunity to foil agri-business - "food is political, and things are going to get worse" - and for another place to write.

She wouldn't mind a bit if people started thinking of her as Rita Mae Brown, author, instead of Rita Mae Brown, lesbian author. "Anyway," she banters, "I'm a lesbian in name only. I'm much too busy to practice what I preach."