Mayor Marion Barry has made a mistake.

In a sudden switch last month, he proclaimed his support of the hotel lobby at the expense of residential neighborhoods and a healthy down-down business district.

The immediate issue is whether the Washington Hilton Hotel at Connecticut and Florida avenues should be allowed to destroy houses and displace some 700 people to make room for a big hotel annex.

One of the apartment houses to be demolished is the Wyoming at 2022 Columbia Rd., no doubt the grandest of Washington's grand apartment houses built before World War I.

The Wyoming is a delightful mishmash of Georgian and beaux-arts. Its theatrical entrance pavilion seems built for a Rolls-Royce ad. The lobby would make a good set for Der Rosenkavalier. Still in near-perfect shape, the apartments have been nominated for the Historic Landmark list. Among the many celebrities who have lived in the Wyoming are Gen. and Mrs. Dwight D. Eisenhower. (I don't know what the general paid from 1928 to 1936, but in 1905, the initial rental pamphlet advertised the most expensive, seven-room, seventh-floor, southern-exposure apartment for $85 a month, including heat and hot water but not gas light.

However, there is more at stake here than displacement and historic preservation. If the Hilton is allowed to expand in a residential area, the Sheraton, the Fairfax and a dozen or so other uptown hotels must be permitted to expand.

The basic issue, then, becomes the city's long-range interests versus big business' short-range interests. Does the mayor really want to spread convention hotels all over uptown neighborhoods and drive even more people out to the suburbs? Shouldn't he steer these hotels downtown to help make the mammoth Convention Center work?

Uptown expansion is cheaper for the hotels, but it will prove frightfully expensive for the people of Washington.

Last summer, Mayor Marion Barry seemed to understand this. On Aug. 4, he told the citizens who were protesting the Hilton annexation plan: "I am against expansion that would displace residents and disrupt neighborhoods. We're together on this one."

On Jan. 17, he let it be known through his planning director, Jams O. Gibson, that he supported this Hilton annexation proposal. It is now before the Zoning Commission, which promised to announce its decision by Feb. 14.

Barry, Gibson and company argue that Washington needs more hotels and more jobs of the kind hotels provide.

Sure.

But the hotels are coming in because there is a demand for them. If we keep them out of residential neighborhoods, like every other city and county in this county, they will still come in. It only costs them a little more, because residential land is cheaper than commerical and because uptown additions save them money on such things as additional restaurants and swimming pools as well as for extra personnel.

The customers would not mind. Research has shown that 86 percent of all Washington hotel guests attend conventions or do other business.They are on expense accounts, and a convenient location is more important to them than a small cost difference.

So, in the end, we will get more hotels, more jobs and happier hotel guests downtown closer to the Convention Center, Capitol Hill, government agencies, corporate and trade association headquarters, the airport and Union Station.

We certainly would get more hotels and more jobs if the city were thriving. It cannot thrive as long as it continues to lose population and business to the suburbs. Barry, Gibson and company must surely know this.

They must know that in the last nine years, the District of Columbia has lost 13 percent of its population -- 101,000 people.

That's not only because people don't like D.C., because the schools are bad, or because they think (mistakenly) that there is more crime here than elsewhere. It is also because the District offers virtually no affordable housing.

If the uptown hotels are allowed to expand, the city will lose another 40,000 housing units, according to conservative estimates. It will also lose livability. Bigger hotels generate more traffic and need huge, noisy trucks.

To permit that doesn't make sense.

Nor does it make sense to let the old downtown central business district become nothing but an office center. But that, as the mayor and Gibson ought to know, is exactly what is happening -- another vast Rosslyn between the Capitol and the White House, dead at night and on weekends.

The large number of new building applications downtown is gratifying. The fact that they are vitrually all for office use is terrifying.

The only way to bring people, night life, bars, restaurants, department stores, little shops, big shops, movies, theaters and other attractions into this office ghetto is to build apartment houses and hotels there.

Some 80 percent of all D.C. office workers commute from the suburbs A lot of them bring brown bags and don't spend a nickel downtown.Offices pay very little revenue to the city. Developers like them however, because office buildings yield nice profits at small risk.

So instead of building more hotels downtown, developers tore down existing ones, such as the Roger Smith and the Burlington, and replaced them with office buildings. There is a great pent-up demand for new office space.

With energetic planning, rather than the present, business-serving laissez faire, the downtown business center could meet this demand -- there are still some 5 million square of space to be developed -- and at the same time, generate life and revenues to meet the city's social obligations.

The way to do this is to create special zones for retail development. With a little effort and imagination, downtown Washington could develop markets and shopping malls that would make the suburban centers shrink with envy and boredom.

The Metro rapid-transit system, with eight stops in downtown Washington, is ready to bring customers from all over the region. Millions of tourists would gladly come out of the museums if only there were something to do, buy or eat downtown.

The Pennsylvania Avenue Development Corp. is thinking in such terms, but its jurisdiction is limited. Gibson's city planning office is meanwhile, busy justifying the mayor's shifts by arguing that hotels have "sleeping rooms" and are therefore a "residential" land users.

They are not -- as the admirable D.C. Citizens Planning Coalition, represented by Ann Hargrove, Anne Hume Loikow, and Lindsley Williams, is telling the Zoning Commission.

Hotels are commerical enterprises; they are an industry.

The only reason hotels marched up Connecticut and Massachusetts avenues was the acute housing shortage during World Wars I and II. At those times, thus city tolerated anything that would put a roof over war time emergency workers.

Now the time has come to sort things out, the Planning Coalition says. It would create a special zoning category for hotels. Convention hotels should be confined to downtown. Smaller, family hotels to accommodate tourists might be distributed judiciously around Union Station, the universities, hospitals and other institutions that need them.

One way to induce big hotels to act as catalysts for imaginative retail centers is what planners call a planned unit developments. That means the city invites developers to draw up a plan for a variety of uses rather than prescribing one. The developers' imaginations are unleashed, and the city can still restrain them if they run wild. The planned unit developments would combine a big hotel with "gallerias" a la Milan, sophisticated shopping, rooftop restaurants and all the rest. Combined office, hotel and retail centers could help create a new Washington.

For the city, the tax yield of retail enterprises is from 5 to 10 times greater than from office buildings of equal size. Retailing creates local jobs. It stays open in the evenings and on weekends. It makes streets safer. It induces conventioneers and tourists to spend money.

In the end, the Hilton will be better off, if it is forced to build a new hotel downtown rather than an annex on Columbia Road.

The city's new Convention Center, to be sure, may eventually compete with the Washington Hilton's convention facilities. But there is a simple, profitable answer to that. The Hilton could convert its ballrooms and exhibition halls into shops and boutiques and convert excess hotel rooms into luxury apartments.

Such a new complex night be called the Hilton Porte d'eau, to put the Watergate to shame.

At any rate, hands off the Wyoming!