Japan's best-selling mystery writer is a shy, bald, little man in his 70s who lives in suburban Larchmont, N.Y., and collects postage stamps. His name is Frederic Dannay and you're probably never heard of him. However his name is also Ellery Queen and you've almost certainly heard of him.

Frederic Dannay rarely appears in public. He is inflicted with incurable stage fright, shyness and modesty. But he surfaced this week at an International Congress of Crime Writers. He got a lot of attention.

Ellery Queen has been appearing in print a long time. Next year is the 50th anniversary of his first novel, "The Roman Hat Mystery." Millions of copies of his books have been sold and the stories have been printed in both major languages.

The exact numbers you won't get from Dannay. Maybe 150 million copies in all, he guesses.Maybe 35 novels and an awful lot of short stories. "Oh, I really don't know: I'm a little vague," he says. "I just work and let the statistics take care of themselves."

Nor will Dannay volunteer that his "The Tragedy of Y" is No. 1 in Japan. He'll tell you all about his trip there last fall; about how he was asked to help introduce the Japanese detective story to the West, without mentioning that No. 1 business. His wife Rose would have to tell you that.

"He's very modest and retiring," she says. "And very surprised by all the attention and love the Japanese people showered on us. He was overwhelmed." The Dannay got married about 2 1/2 years ago, and Fred is so modest that it was only several weeks after they met that Rose found out about Ellery Queen. Fred never mentioned it. Someone else told her. "He would never talk about himself that way," she says.

Nor would he never talk about himself this way: "Fred Dannay is the American mystery story." But several other people were perfectly willing to make such conversation around the Baltimore Hotel where the mystery perpetrators were conspiring. Such talk referred not just to Ellery Queen the writer, but Ellery Queen the editor.

A brief pause to unthicken the plot the name "Ellery Queen" embodies enough literary indentities to confuse any bloodhound. First there's E.Q. the detective, protagonist of all those novels and stories. Then there's the E.Q. listed as the author of same. (This was a clever and original intention. "Our thought was it would be twice as easy for people to remember," says Dannay). The E.Q. books were actually written by two people: Dannay and his cousin. Manfred B. Lee, who died in 1971. No new novels have appeared since.

And there's yet one more E.Q. of significance: Ellery Queen Mystery Magazine. It's considered the most prestigious showcase for mystery writers. Dannay founded it and has edited it for its full 37 years. "That's probably a world's record for a mystery magazine," he says.

Thought Fred Dannay is unknown to the public, he's very well known to his fellow mystery writers. In his role as E.Q. magazine editor, he launched many of their careers. "He's extremely kind of generous," says Donald A. Yates, a Latin literature professor at Michigan State University and a mystery fan.

"He's helped countless people. He's published more than 500 first stories by writers. His influence is extraordinary. No one has gone more than Fred Dannay for the American detective story."

Otto Penzler, a mystery publisher (The Mysterious Press) and editor, goes further. "Without Ellery Queen," he says, "the mystery short story would have died."

Dannay spends most of his time editing the magazine these days. It has certain literary claims, by the way. It has published five Nobel Prize winners and numerous Pulitizer winners. William Faulkner wrote for it and Katherine Anne Porter. George Luis Borges published his first story in English in E.Q. It is the New Yorker of the mystery story.

And Dannay takes his commitment to find and develop new writers very seriously. He was sitting on a panel the other day with other magazine editors and there was talk about some magazines not reading "slush" - publishing jargon for those mountains of unsolicited stories sent in by unknown writers.

"Every story submitted must be read," said Dannay with passion. "The importance of slush cannot be overestimated." He mentioned some of the writers, now well known to mystery readers, he had first published. "The slush pile represents the lifeblood of the future. Who else will take the place of the so-called ole-timers?"

You wouldn't have known from listening that Dannay was in a sweat up there. He sounded confident and in control. Later, though, he said it was bad. "Even getting on a panel is a great dread to me. I don't like public appearances. I've done everything I can to cure myself, but nothing works."

But the shyness has its good sides, he reflected, for a detective writer. "It added a note of mystery in the beginning.It hepled."

The beginning was in New York in 1929. Dannay, who'd grown up in small upstate city of Elmira (his father was in the liquor business until prohibition, then switched to tailoring), had come to New York to work as a copywriter in an ad agency. He and his cousin noticed an ad for a magazine contest. Write a mystery novel, it challenged. They were both interested in the form. They'd been reading the highly popular Philo Vance detective stories of S.S. Van-Dine. "As a lark we went into it to see what we could produce," said Dannay.

They produced E.Q. Ellery was the name of Dannay's oldest boyhood friend. Queen just sounded right after wrote another E.Q. They made some modest money but by now the Depression was on. Their agent advised them to fish or cut bait; they couldn't go on working their day jobs and writing by night, he said. "So being foolish young men, we quit," said Dannay, "and the rest, as they say, was history."

The E.Q. novels have gone through several distinct changes in their long history. In his first incarnation, Ellery was something of the pompous dandy. (He often called his father "Pater.") But some fans consider the early E.Q.'s classic examples of the mystery form. In his middle period, Ellery became a more realistic character and gained a measure of social consciousness. And in the third phase, the third, the books became less purely detective Genre and closer to straight novels.

Yates, who is planning a biography of Dannay, calls the Dannay-Lee partnership "the most important literary collaboration perhaps ever - the only thing that approaches it is Gilbert and Sullivan," and feels that as literature the E.Q.s are among the best written detective fiction.

"The hallmark was complete and absolute fairness to the reader," says Yates. (The reader oftentimes had to find the current obscure fact to unravel the mystery.) "Ellery Queen never knew more than the reader knew. And there came a point when they stopped the plot and inserted a challenge to the reader - Ellery Queen now knew who committed the murder and the reader was challenged to guess who it was."

The mechanics of the Dannay-Lee writing method remain the unsolved Ellery Queen mystery. The authors never talked about who wrote that and Dannay still won't. "People have made all kinds of guesses," he tantalizes. He says he is now working on a new E.Q. novel. But he is also trying to cut down his work load.

Dannay has had his troubles in recent years. His wife died not long after his cousin had passed away. "That was a bad hiatus," he said. I'm not a person who finds it easy to be alone." But then he met his present wife at a dinner party. Caught Freudian-slipping, "I'm not as old as I used to be," what he meant to say "young," Dannay allowed as how marriage has cheered him up. We're practically newlyweds," he says, holding hands with his wife. He may be the retiring type, but he sees no retirement from work ahead. Just more editing mainly which he does at Larchmont where he's lived about 30 years.

The manuscripts and memos go back and forth to the office by messenger. Fred Dannay doesn't like to get into New York much.

But there he was this week, basking in the affection of his colleagues, and just once at least giving them a taste of their own medicine. Sitting in that panel discussion, Dannay remarked in passing that the E.Q. magazine had once published, from a German author, a story just one word long. Dannay and the panel went to other matters but his small time bomb lay ticking in the squirming audience. More suspense from Ellery Queen. You could sense that few minds were fully on the discussion. Finally they could stand it no longer. "What was that word?" someone shouted.

"Bang," said the master of the mystery, and added, "with an exclamation point."