Working WASP Washington is a pin-striped, natural-shoulder, two-button town.

An occasional polyester populist gets elected to Congress or slips in through the back door of the bureaucracy, but the male members of the indigenous fauna are incarnated in all-natural fabric. Even in August the tropical wools outnumber the hardy Haspels at the watering holes of Connecticut Avenue and K Street NW.

No self-respecting WASP would ever shed a suit coat in public, so only his haberdasher knows for sure where he shops.

A peek beneath the lapels will almost certainly reveal more Raleigh's labels than anything else--and more Sy Syms specials and Dash's Designer discounts than anyone will ever admit to buying. But for pure, hand-tailored cachet, Washington men on the move (as opposed to on the make) have traditionally turned to Lewis & Thos. Saltz, Britches of Georgetowne and Brooks Brothers.

Ordinarily, shopping habits change even more slowly than men's fashions, but the city's traditional menswear business is now in the midst of a subtle revolution.

No, the Full Cleveland is not making a come-back; not even the California-clad Reaganauts have driven fashion that far afield. The leisure suit is still dead, designer jeans still dying. Commander Salamander has not yet captured the Chevy Chase Country Club crowd.

What's happening is that Britches has been sold, the Saltz stores are for sale and a new name, Waters & Waters, will soon start showing up on the inside pockets of proper pin-striped jackets.

On Friday, the two founders of Britches, Rick Hindin and David Pensky, disclosed that they have sold their 19 stores to CML Group, a Boston consumer-goods conglomerate whose best-known brands include Boston Whaler boats, Sierra Design parkas and Carrol Reed ski wear.

Though the word on the street is that the deal has made millionaires of Hindin and Pensky, informed speculation is that the big profit is mostly on paper. Hindin and Pensky will continue to run the stores they founded 16 years ago and will become important stockholders in CML.

How much stock they got is likely to be disclosed in a few months, when the Boston company plans to sell shares to the public. Britches considered going public on its own, but the principals may do even better as part of CML, a collection of merchants catering to the shoppers Britches knows best--affluent, under-45 over-achievers.

The Britches sale will not only allow the two founders to cash out some of their success but also will provide capital to double the size of the business in the next five years, an ambitious goal even for a chain that is able to run two stores in most local shopping centers.

Different reasons are behind the potential sale of the Saltz stores, which have been on the block for some time. The Saltz family, of course, has been out of the business since 1955, when Thomas switched to the Georgetown University Shop. Their successors, a family group headed by Richard Steen, sold the stores for about $3 million in 1977. Since then, the Saltz stores have been run by Stanley Rosensweig and his partners Theodore Lerner and Albert (Sonny) Abramson, the developers of White Flint, Tysons Corner and dozens of other projects.

A year and a half ago, the Saltz stores at Tysons Corner and in Chevy Chase were sold to Brooks Brothers. It's an open secret that Lerner and Abramson are entertaining bids for the remaining units--at White Flint, 1009 Connecticut Ave. NW and 1409 G St. NW., though the Saltz store owners adamently refuse to discuss their plans.

At least one New York buyer considered taking over the Saltz operation, and others have offered to buy some of the real estate. The White Flint Saltz location is usually regarded as the best store location and the worst store layout in the batch. It is also the most important bargaining chip for Abramson and Lerner since they own White Flint and could easily install another merchant in that space.

A bid for the Connecticut Avenue Saltz store site was made earlier this year by David Waters, the former chairman of Garfinckel, Brooks Brothers, Miller & Rhoades Inc.

Ousted after unsuccessfully and unsubtly opposing the takeover of GBBM&R by Allied Stores in 1981, Waters plans to start a new menswear chain in partnership with his brother. Waters & Waters will plunge into direct competition with Saltz, Britches, Brooks Brothers, the Ralph Lauren/Polo shop, the Georgetown Shop and the rest of the pin-stripe purveyors.

Besides an impeccable sense of personal style, Waters has a knowledge of the Washington WASP menswear market that few can match, gained as chairman of the parent of both Garfinckel's and Brooks.

Because of moves made when Waters was still there, Brooks Brothers' share of the local men's business has increased significantly in the last couple of years, surely compounding the problems of the Saltz stores.

Brooks' downtown volume has jumped since the store moved from its second floor location at Connecticut and L streets NW to a prime corner at 18th and L. Even bigger increases in sales came as the result of acquisition of the Saltz locations at Tysons Corner and in Chevy Chase.

Knowing both Washington and Brooks Brothers as well as he does, Waters ought to be able to build a formidable competitor. Knowing Waters, he won't settle for a comfortable little corner of the market.

Nothing as unseemly as television advertising or pin-stripe price wars is likely to result from the increased competition in the upper-crust menswear market. But like the men who wear $400 suits, the men who sell them aren't in business for the fun of it.

No, Marriott Corp. is not going into the menswear business, but don't be surprised when J. W. Marriott Jr. turns up wearing a Hathaway shirt--and an eye patch--in fall fashion advertising.

Hathaway is bringing back the famous patch ads, and its Madison Avenue agency figured the best people to sell shirts to businessmen are businessmen. Beside the Marriott chief executive, the men in the Hathaway shirt (and patch) will include Ted Turner, the cable TV mogul, and John Naisbitt, author of "Megatrends."

The shirt campaign is a mini-trend at most, but Marriott watchers note that young Bill Marriott has been carefully raising his profile over the last several months. Taking a lesson from Frank Borman of Eastern Airlines and Lee Iacocca of Chrysler, Marriott is personally pitching the company's hotels in ads aimed at business travelers.

American Express ought to pick up Marriott next. What better endorsement could there be than to have the man whose name is on the door of 120 hotels say he wouldn't leave home without his American Express card?