Last year, a Smithy Braedon Co. official, writing about new opportunities in the retail industry, used a pointed aphorism that probably best describes the demise of Lewis & Thos. Saltz Co.: "One retailer's poison is another retailer's medicine," wrote Armond Spikell, a specialist in the sale of shopping centers.

In Saltz's case, the poison began to take its toll on the venerable retailer several years ago. Confirmation this week by Saltz officials that the retailer was closing its last store after half a century was only a formality. Retail industry sources had speculated for some time that the end was near.

Saltz's officials blame the high costs of leasing retail space in the downtown Washington store for their decision to go out of business. With a long-term lease about to expire at the Connecticut Avenue location, and the renewal rate substantially higher, "We found out we couldn't continue in business in this spot," an official told The Washington Post this week. "We found we had to vacate our location" because of the real estate business, he added.

That implies that retailers' profit margins may diminish as the real estate business demands more money for prime space in one of the country's hottest commercial markets. The explanation given by Saltz officials further implies that there is no viable alternative to the soon-to-be vacated Connecticut Avenue location; that Saltz would cease to be a viable competitor in another building in the same area, in another part of town or elsewhere in the area.

The history of retailing in metropolitan Washington over the past decade suggests that Lewis & Thos. Saltz Co. ceased to be competitive among men's apparel retailers several years ago.

The mere fact that the company -- once a prestigious men's store -- is left with only one store says a great deal about its decline at a time when not only specialty apparel stores, but retailers in general, continue to expand in a highly competitive and lucrative market.

The high costs of space notwithstanding, successful retailers aren't throwing in the towel in the Washington market. At the same time, the rising costs that made the rapidly changing market poison for Saltz apparently haven't blunted the market's appeal to out-of-town retailers, judging by recent announcements of plans to open new department and specialty stores.

More than 11 million square feet of retail space were built in the Washington area between 1980 and 1985. That in itself is testimony to the fact that metropolitan Washington anchors the country's fifth-largest consumer market.

Notwithstanding the fact that retail sales fell sharply in the District in the decade of the 1970s, the city's share of retail sales growth during the early 1980s (26.9 percent, according to the Greater Washington Research Center) compared favorably with growth in most area jurisdictions.

A recent study by the Metropolitan Washington Council of Governments shows that the region's economy exhibited "a growing retail sector in both jobs and sales volume" between 1980 and 1985. The analysis indicated that retail sales for that five-year period increased by $3 billion, after adjusting for inflation.

In the midst of that growth, Saltz's principal competitors seemed to have had a better feel for the demographics of a rapidly changing market. Raleighs, the area's leading men's retailer, enhanced its merchandise lines and expanded under the previous owners. The new owners have improved on that strategy.

Meanwhile, Britches of Georgetowne has carved a substantial market niche. And Brooks Bros., Saltz's main competitor in the pricing and merchandising of more traditional clothing, has obviously won that competition hands down. Other menswear retailers, several of them new to the area, "have positioned themselves well," observed a retail executive.

"I think we can look at Saltz over the last several years and conclude that management didn't know what it wanted to sell and who it wanted to sell it to," said the executive, who declined to be identified.

Saltz's search for a market and an identity began in the 1970s when the company was sold.

The search continued after it was sold again in 1983 to investors who knew little about the Washington market but assumed that the Saltz name and, perhaps, the addition of a new merchandise line, would assure customer loyalty.

The company may have shown a "180-degree turnaround" within the past year, as one Saltz official asserted. But a review of events preceding the turnaround suggests that Saltz's current owners misread the market and what it takes to be successful here.

The demographics of the area make it attractive but, as Spikell cautioned, this is a "very tough, competitive market . . . . Washington consumers are a sophisticated lot and retailers must deliver quality and value if they are to survive in this climate."

Understanding the market helps.