You could tell right away that the approaching lecturer was a CIA type: He walked across the snow and left no footprints. He said his name was "Tom Clancy," but everyone knows there are hundreds of "Tom Clancys" at the agency using thousands of cover stories. Then he declared that he was really an insurance broker down in rural Calvert County, where that big nuclear reactor pulses, and that he got an English degree at Loyola College in Baltimore. Ha.

But the part of his "legend" that most strained credulity was this: "Clancy" said someone paid him $35 to write a letter to the editor a couple of years ago and so he became a writer. Then he said he wrote a novel called "The Hunt for Red October" that has sold 45,000 copies, and it wasn't even published in New York. And he did this without a literary agent!

Tell us another one, pal.

Thomas L. Clancy Jr., 37, who uses the sobriquet "Tom Clancy," started writing "The Hunt for Red October" in July 1982 "from the beginning, not knowing how it was going to end. It really was a lot more fun doing it that way . . . If you plan things ahead of time you lose spontaneity."

Thus flying in the face of hallowed literary tradition, he created a story based on the 1975 attempted defection to Sweden of a Soviet destroyer crew. From that event, and a few others, Clancy crafted a fast-paced, strongly plotted and technically solid account of a half-Lithuanian "sub driver" defecting to the West with the Red October, the Soviet Union's newest, stealthiest and most powerful nuclear missile submarine.

"I knew I could look up the facts," Clancy says. "What I didn't know was what kind of people go to sea in ships that are designed to sink." He found out by interviewing submariners and technical experts.

Since publication by the Naval Institute Press in Annapolis last October, "The Hunt for Red October" has had four press runs and hit best-seller lists in Washington, San Francisco and New York City. The Naval Institute Press is preparing a fifth edition of 25,000 copies.

Because "Red October" has sold 45,000 copies, publishing experts call it a "stunning success." (Most first novels by unknown writers sell 3,500 to 5,000 copies.) Considering the additional barriers Clancy faced -- no agent and a nonfiction publisher that had never before produced a novel and lacked the brute-force sales and distribution machinery of the New York houses -- "Red October" also could be called a breakthrough.

Word of mouth and more than a dozen reviews, some enthusiastic, propelled sales. Paperback rights went to Berkley Publishing Group for $49,500 and United Kingdom rights went for around $15,000. The Naval Institute Press has sold foreign language rights for Dutch, West German, Japanese and South American editions.

"We don't have any pretensions that this is great literature," says Naval Institute Press marketing director Jim Sutton. "It is just a hell of a good read."

"O.F. Bowen Agency," Clancy answers the telephone.

This is Clancy at work. He writes policies as well as books. In the summer thousands of people drive by his office at the Bowen Agency in Owings on Maryland Rte. 260 on their way to Chesapeake Beach, four miles down the highway.

"When did you last have a policy with us?" he asks a caller. "What is your name? How old are you?" Clancy and his wife, Wanda, who operate the agency, have 1,000 clients in Southern Maryland.

On the floor of Clancy's office is a large blue bag that houses the Apple Macintosh computer he composes on when there's down time in the insurance business. Along the walls are war games, books on weapons, and government-produced maps of Germany he is using to write his second novel.

"When you're your own boss," Clancy says, "you can budget your time." If writing weren't fun, Clancy says, "I wouldn't do it. I don't need the money. This business supports me rather well."

Among Clancy's insurance clients are people he calls "nucs" -- pronounced "nukes" -- former Navy nuclear engineers who operate the Baltimore Gas & Electric Co.'s Calvert Cliffs Nuclear Power Station on the Chesapeake Bay, 20 miles south of the Bowen Agency. Clancy mined them for technical information about the nuclear and naval aspects of "Red October." He says the Navy's "nucs" are "the best in the world."

Clancy is well read in his genre of thriller novels. He says Frederick Forsyth "is, at his best, probably the best in the business. Richard Cox, he hasn't done much work but what I've seen I really like. Jack Higgins, at his best, he's awfully, awfully good. A.J. Quinnell a pseudonym , the new guy, nobody even knows who he is. There's a number of good writers out there; fortunately or unfortunately, most of them are Brits and I figured it's about time an American did it."

The central character and hero of "The Hunt for Red October" is CIA analyst and historian Jack Ryan. Ryan, a clean-cut all-American, "started to take form in the late 1970s," Clancy says. "In most any thriller fiction, the hero is an unmarried guy in his thirties who likes to drink and smoke and run around . . . What's wrong with a hero who's married, loves his wife and plays with his kids? That's what most people are," says Clancy.

Like Clancy, Ryan was born in Baltimore, but here creator and createe diverge.

Ryan, Clancy explains, "got a degree at Boston College in economics and went into the Marine Corps, was injured and retired on a medical discharge, along the way he got a CPA, went to work for a stock brokerage firm, made himself a lot of money . . . married a doctor, an eye cutter -- Kathy Ryan is an ophthalmic surgeon -- and then he decided he was just going to leave the brokerage business and got himself a doctorate in history . . . and through a circuitous route he found himself being invited to join the CIA."

There is no room, in Jack Ryan's world, for doubters and second-guessers. Ryan himself is a self-assured man of mental and physical action. Jack Ryan's activist CIA, in contrast with portrayals by some other espionage writers, is not immobilized by fear of Soviet moles. It's the reverse: Ryan's CIA runs our mole in the Kremlin.

"When America deals with other parts of the world," Clancy says, "we should concern ourselves less with what we're against as opposed to what we're for. Too often, conservatives, you always hear what they're against and there's a reverse side to that. We are for freedom, we are for justice, and the reason that we and the communists can't get along is the reason that they are not for freedom and they are not for justice. They are the negative guys and we are not."

For his next work, Clancy has teamed up with a naval analyst, Larry Bond, to write a book tentatively called "Sunset."

"It has a naval subject matter and it's quite a bit more complicated than 'Red October,' " Clancy explains. His plans after "Sunset" call for three more Jack Ryan thrillers. The first of them is called "Patriot Games," Clancy says, and deals with terrorism and the period of Ryan's life that preceded the events in "Red October." Clancy may have been an untested novelist when he wrote "Red October," but he still had the good sense to lay the groundwork for a sequel.

"I'm not that good a writer," he says. "Maybe I will be some day but that day is not yet in sight . . . I do a good action scene. I handle technology well. I like to think that I do a fair -- fairer -- job of representing the kind of people we have in the Navy . . . portraying them the way they really are. Beyond that, I'll try to listen to my critics and improve what needs improving."

Having concluded his lecture in a Loyola College classroom, "Tom Clancy" has faded away into snowy Baltimore. The darkened room is empty except for a curious spectator hunting for clues to this man's identity. On the lectern he spots something under a few scraps of crumpled paper. It's an ID card enclosed in plastic. Being careful not to leave fingerprints, he picks up the card and examines it. Printed across the front, in red, white and blue, he sees the words, "Official Literary License." His search ends suddenly when his eyes drop to the next line.

The card was issued to Jack Ryan.