The man in the tattersall vest and the Brooks Bros. suit may be outfitting at Abercrombie and Fitch in New York City. Or it may be a chap in shorts and thongs on Lincoln Road in Miami Beach.

Or a chap in western sombrero and boots in a Denver sporting goods store.

If they are planning a trout fishing jaunt and ask advice of a knowledgeable salesman, likely they will leave with a Dan Bailey fly - perhaps a Grizzly Wulff, if dry fly fishing is their bent, or a Muddler Minnow for wet fly fishing.

For Dan Bailey, former college professor, a native of Kentucky who taught on the college level 10 years, the last eight at Brooklyn Polytechnic, has found himself recognized in the last 20 years as a world famous authority on trout flies.

It came about, he relates with a bemused smile, through a river, outdoor writer friends and the proverbial better mousetrap.

Bailey was born near Russellville, Ky., March 22, 1904, graduated from The Citadel in North Carolina and received his masters in physics while a graduate assistant at the University of Kentucky.

"He recalls getting interested in tying flies, being an ardent fisherman, and soon people were buying his flies. "It became a sideline business," he says.

First the flies, then the river - the Upper Yellowstone in Montana which he first fished while on his honeymoon in 1936.

The Baileys returned in the summer of 1937 and he still liked the Yellowstone from its headwaters in Yellowstone National Park to around Big Timber. In the spring of 1938 Dan moved to Livingston and established Dan Bailey's Fly Shop.

It was slow at first. He ties the dry flies and bought the wet flies. Soon the boys around town came in and wanted to help. Now he has a huge mail order business and 30 women working on a fly tying assembly line.

The women came when one of the town boys took home some work and his mother helped him. His mother's flies were better than the boys, says Dan.

Now his staff ties from 400,000 to 500,000 quality flies a year.

The reason Bailey came to Montana became the reason for his success. After a slow start, the Yellowstone River was being discovered by outdoor writers. Many were somewhat tired of the Madison, most highly touted of the West's blue ribbon trout streams.

And outdoor writers, among them Joe Brooks, discovered Dan Bailey and his flies.

"It was a slow climb ... I guess my first national break came from an article in Fortune magazine in 1946, written by my old eastern fishing partner, John McDonald," Dan relates.

McDonald apparently also profited by the article. Written while he was freelancing, he is now editor of the same magazine that gave Bailey his national start.

Then came Brooks, who also fell in love with the big Yellowstone. There was a shy chap named V.T. Hamlin, who has a friend he also credits for his start. The friend, of course, is Alley Oop, for Hamlin is the artist for the comic strip and spent many a happy summer floating the Yellowstone.

There were others. "I remember a funny, shy little guy that used to come around and buy gear and talk fishing. We finally found out he was Garry Moore."

In addition to friends, the Yellowstone and the better fly, Bailey has another thing going for him.

It is the Wall of Fame where the outline of the big fish taken in the area are marked on plaques on the wall of the shop.

Limited to trout over four pounds, there are now 286 on the wall. "We had to limit the plaques to one a fisherman, we ran out of wall," he said.

Biggest fish on the wall is 17 pounds, 10 ounces. Another that draws some attention is a six pounder, caught by Bailey himself.

But there is always, pardon the expression, a fly in the ointment.

Says Dan Bailey, tyer of flies for the famous: "I'm so darn busy I don't have time to fish."