Inside almost every political speechwriter lurks an author struggling to get out. Joseph Persico came to Washington in 1975 as chief speechwriter to Vice President Nelson Rockefeller, but unlike some of his brethren, he escaped the institution to become a successful author.

His first book, Piercing the Reich, told the story of the penetration of Nazi Germany by the OSS. Viking published it earlier this year and sold paperback rights for $130,000. Persico's first novel, The Spiderweb, will be released by Crown in October.

"Three weeks after I'd gone off on my own," Persico recalls, "I went to New York on an interview for Piercing the Reich. I was sleeping in a friend's apartment and had this dream in which I was talking to a man on a park bench in Washington, and he said, "What do you do?" I told him I was a writer and he said, "What a coincidence, I am too. I've been doing it for 25 years and I've made $50." And suddenly I woke up in this cold sweat and asked myself what the hell was I doing?"

Adds Persico: "I was a guy who'd been all of his adult life in somebody else's harness, and there was a certain amount of sour-searching. I had two qualms: ages 17 and 15, two daughters who would be going to college soon."

But armed with a contract for his first book and the reassurance of a wife who worked, Persico walked the plank. Using the Freedom of Information Act he extracted documents from the CIA ("an elegant form of dentistry," he says dryly) that described America's deep infiltration of Hitler's Germany. Material left over from that task provided the basis for his World War II suspense novel due out this fall. Today, the 49-year-old Bethesda resident regrets he didn't leave the shadow of Rockefeller earlier. He's made more money, and he's happier in his work.

By coincidence, Persico began promoting his first book soon after Rockefeller's death.

"Here I was with a serious war book slotted between an 81-year-old yoga queen and a Jane Russell look-a-like contest," he says of one promotion appearance in Los Angeles. "I'd be talking about infiltration of secret agents and then I'd be hit with, "Did you know Megan Marshack?" and "What did happen there at the end?" I became the most sanctimonious guest imaginable. I'd say, "I really think that kind of gossipy speculation is beneath the caliber of your show," and I immediately thought, "If I'm going to talk about those things, it'll be in my own book, and not on your show.""

That's spoken like a true author, and, in fact, Persico says he is weighing offers to write about his experiences with Nelson Rockefeller. But first he's preparing to sell a second novel, "a sexual, sociological thriller set in the future," which only his wife has read.

Persico begins his writing days jogging for half an hour in front of a television set turned to The Today Show. If he's writing non-fiction he writes in longhand; for fiction he uses a typewriter.

"Don't laugh," says Persico, "I can make sense of it. To me, writing non-fiction is uncovering a story already there. It's a much slower pace of creation. I'm much more comfortable flipping through my cards and books and writing in longhand.

"The creative process of writing a novel is wholly different. Here is an explosion of the imagination, and I can't keep up with the pace in longhand."

The life of a free-lance writer can raise eyebrows. With his wife working and his daughters in school, Persico is the last to rise in the morning. Once, his 14-year-old daughter stood over her father's bed, gave him a mystical smile and said, "Daddy, if you had a real job, you'd be getting up now." CAPTION: Picture, no caption, by Joel Richardson