ALAN Rubin owns half of the Biograph cinema in Georgetown, but he's staking out a second career with a Rapidograph pen. He's just published his first book, "Gopher Broke" (Harmony Books), a sprightly collection of often agonizing visual puns. Rubin recalls that when he was seven years old "my pediatrician was Austrian--this is real--and he came to the house, took out his tongue depressor and told me to open my mouse. For some reason, I thought that was the funniest thing I had ever heard an adult say. That was the first pun I ever heard and I just liked that kind of humor from then on."

Rubin calls his work "punjabs, where the caption is a common word or phrase but the drawing is not quite what you think of at first. It's more a quirk of perception."

A geologist by training, Rubin came to Washington to work with the U.S. Geological Survey, also picking up his master's degree at George Washington University. Sixteen years ago, he and four other friends, all in their late twenties, decided to open a repertory film house. Voila, the Biograph.

Rubin is not a novice to the publishing world: 12 years ago he self-published a similar volume with a friend. "That one was all related to hearts and arrows," he recalls, "very visual, and very primitive compared to what I do now. I did all the drawings, the color separations, printed 500 copies and went around to stores to get orders. My friend and I also dressed up as salesmen and went up to New York to the offices of Woolworth's. The buyer said, 'I think I'll test-market them,' and asked how we sold them. We said boxes of 50, and he said he'd take 300. 15,000 books we sold! Our hands were shaking."

That book, which became a Valentine's item, ended up selling 40,0000 copies. "We used to package them in our basement and deliver them by truck; we did the whole process from design to delivery, and learned a lot about how the publishing business functioned."

The affable Rubin, who had for many years drawn for his friends' amusement, finally got around to doing a portfolio last yearand submitted it to several publishers through a friend, literary agent Betsy Nolan. Nolan, who also handles James Clavell and Wendy ("Thin Thighs in 30 Days") Stelling, "shopped it and became my agent." Harmony Books bought it, and it's already in a second printing.

"I wrote it in drive time," Rubin says, commuting from his home in Delaplane, Va. "I developed about 600 puns on the way back and forth from work, and then did about 200 drawings . . . not in the car, of course." Sixty of the pieces were published in "Gopher Broke" and a second book has already been submitted.

He'd like to move from books to a single-panel daily comic strip, "a 'Dennis the Menace' or 'The Far Side' type of thing, but it's so tough. The syndicates get 7,500 submissions every year, and take on only seven or eight, so it's literally odds of 1,000 to one . . . but coming in with a successful book might give me a better shot."

Susan Rubin, his wife and a coworker in the Biograph's distribution arm, has also found a new niche that takes her from behind the scene to on screen: that's her playing the princess' mother in Tom Davenport's "Frog Prince," a live-action short that occasionally shows at the Biograph. Davenport is a Delaplane neighbor.

In recent years, the Biograph has pursued a festival format, and Rubin loves to tell a story about a close encounter with a screen idol. Two years ago, he organized a very successful Katherine Hepburn/Cary Grant festival, and when Hepburn was at the Kennedy Center last spring in 'West Side Waltz,' Rubin, a long-time fan, sent her a note and a festival program. Next day, he got a call from Hepburn's manager: expecting kudos, he was instead lambasted. " 'Miss Hepburn does not do ads!' he said. Well, we have ads on the back of our program notes and we'd taken a photo of Kate and Cary from 'The Philadelphia Story,' a shot of him with her looking over his shoulder. We put a six back in his hands and had a caption saying 'Tonight, let it be Lowenbrau.' I'd forgotten all about that."

"Well, we got 80 bucks for the ad, but her lawyer was going to sue. He wanted a letter of apology, but I forgot about it. Then Susan ran into her at Cannon's fishmarket the day after she'd won her Academy Award, and as Hepburn was getting into her limo, Susan said who she was and reminded her; Hepburn raises her cane, and says 'Shocking, shocking!' She'd just won the Academy Award, you'd think she'd have something else on her mind. The next day her manager called again, so I wrote a long letter, apologized effusively, pointed out it was springtime and the cowlilies were in bloom . . . We drove around to every florist in town, and finally got a big box of cowlilies and sent them with the letter. She sent me back a lovely letter, which I now have framed . . . with the ad. Now if only Cary Grant would send me a letter."