Sue Hays, wife of the Hecht Co.'s board chairman, recently tried to buy some long underwear at one of the Hecht Co. stores.

She learned what many other chilly people lately have discovered: wearing long underwear is so "in" this winter that many merchants have run out of their stock.

Previously popularly with lumberjacks, traffic cops, construction workers and winter sports enthusiasts, "long johns" are losing their Farmer's Alamanac image as many customers especially women, are buying them to wear inside cold offices and homes.

Mrs. Hays later managed to buy four pairs of long underwear at Hecht's, though her husband, Thomas, said the department store chain "is selling out as fast as our stocks are comin in."

Hays said Hecht's has sold 2 1/2 times as much long underwear this winter as last and probably could have sold times as much if it had been available.

The story is about the same from other retailers. A J. C. Penney official said its local stores have at least tripled their usual long underwear sales. Sears Roebuck estimates a 40 per cent jump in such purchases this winter . A Woodward & Lothrop spokesman said his store was "99 percent sold out" of long underwear.

"If I had them, I could sell all we had," said Charles Givens, a Woodies buyer of long underwear. Givens said long john really got scarce here around inauguration day when "we kept getting requests form people with Southern accents and people from California."

F. A. Huntley, resident of West Knitting Mills in Wadesboro, N.C., a major manufacturer of long underwear, said his plant hasn't been able to keep up with the demand across the country during this unusually cold winter.

Huntley recalled that he learned the hard way on a recent trip to New York how valuable his products is. "I'd a liked to froze. What a fool O'd been, making my own product and then not wearing it," the manufacturer said.

Nothing that the temperature was 68 degrees in his North Carolina plant, Huntley said during a telephone interview, "I've got a pair on right now."

long underwear ranges in price from under $4 to $16 or more a pair, depending on style and store. Most common is the two-piece thermal underwear in a standard white. But there also is still some demand, particularly among catalogue purchasers, for the one-piece "union suit" with a flap opening in the seat.

Especially at ski shops, long underwear can be bought in bright reds, pinks, blues and yellows, as well as in prints with skiing scenes, assuming any is still on the shelves. The Irving's Sports Shop at 10th and E Streets NW has been out of longies for nearly two weeks, a salesman there said.

Purchasers of long underwear at sports stores are as likely to be office secretaries as downhill skiers.

A J.C. Penney store in Lancaster Pa., recently received 1,200 sets of long underwear, selling 300 of them in the first hour they were available.

"This type of merchandise sells with the weather," noted James Gettys, president of Standard Knitting Mills in Knoxville, Tenn., another long underwear manufacturer. Because of previously mild winters, there had been large inventories of the product, he said.

Gettys said retailers around the county are hesitant about ordering more long underwear unless they can be assured that it will be delivered immediately and not after the snows melt, leaving them with and unwanted stock until next December.

Long underwear manufacturers insist that this season's big demand for their product hasn't raised the prices, which were set beforehand. However, Gettys said prices will go up before next winter because of an increase in cents of cotton from 55 to about 80 cents a pound.

Huntley said he was surprised to learn that this plant sells more long underwear is presumably sunny California than in anyother state.