"I DON'T EVEN GO NUDE on the beach," said New York literary ag ent Diane Cleaver by way of explaining her presence, sans clothes, in the current issue of Playboy Magazine. That's Charles R. Collum, the photographer from whose new book, New York Nude (Amphoto), the picture of Cleaver is taken--"had me rounding up people to pose and their attitude was 'if I'm going to do it why not you since you're asking?'" Actually Cleaver is in a group shot, with six others from the Sanford J. Greenburger agency where she works, including Francis Greenburger, who heads up the business his late father founded, and Peter Skolnik, author of Jump Rope! There are 117 people and two dogs in New York Nude, but Cleaver and her colleagues (whose clients include Lynn Caine, Ovid Demaris, and Kenny Rogers) are the only ones from a literary agency.

Among the New Yorkers who disrobed for Collum are the aerialist Philippe Petit, musician Richie Havens, Prince Egon von Furstenberg, Elvin McDonald ("an internationally syndicated gardening columnist"), a Saks Fifth Avenue salesman, a former Miss Norway, an all-girl basketball team, a "firebreather, magician and escape artist" a police officer, an investment banker and the chairman of the philosophy department at the Brooklyn Center of Long Island University. There are also three sets of twins. "My doctor, my lawyer, my gym trainer and of course my agent are all in the book, and maybe a few friends, but the rest are strangers, many of whom I just approached on the street. Washington Square was a wonderful place."

New York Nude is a sequel to Dallas Nude, which Collum first published himself in 1977 when he was living in Dallas and working as a commercial photographer. His next stop is Los Angeles where he says it should be even easier to get people to take off their clothes. But Collum's real dream is a double volume set of Washington and Moscow, with the dedication reading "To Peace on Earth."

He even phoned the State Department to see what they thought of his idea there, and an official discouraged him from setting his sights on Moscow. Maybe Prague, he was told. Still, Collum gave the Russian embassy a try. Not surprisingly, though he reached someone on the phone, he didn't make much headway.