HOME-RULE government for the District of Columbia was designed by committee, and thus was a somewhat homely infant. For years, the real power centers of Washington regarded it as ineffectual, immature, ungainly. But there is a host of evidence that Washington's local government has reached a new stage of political maturity: Its attentions are now worth trying to buy.

The mayoral election offers a window onto this new state of affairs. Candidates are -- by Washington's standards -- awash in cash, and the quite natural assumption is that the people investing all that money have hopes of getting something in return.

Betty Ann Kane had to drop out of the mayor's race, citing fund-raising troubles -- she had only been able to raise about $200,000, not much less than the amount that got Marion Barry elected four years ago. John Ray, definitely a second-tier candidate at this point, has already spent $200,000. Patricia Harris, hardly a household name in terms of local political involvement, has already taken in $300,000, and her campaign might top half a million before election day.

But Harris' strong showing pales before Barry's astounding fund-raising performance. As of the most recent reporting date, Hizzoner, the new Sun King of campaign contributions, had raised nearly $700,000, an almost embarrassing sum for a D.C. politician. It is not inconceivable that he will top the million-dollar mark. Barry, Sterling Tucker and Walter Washington together only raised just over a million dollars in 1978. This year's candidates seem sure to double that figure, a fact that signals a real change in local politics.

This cash is coming from lawyers, accountants, bankers, businessmen, developers -- the kind of people who used to have to ask directions to the District Building, but who could walk blindfolded through twisting Capitol Hill corridors to the offices of the congressmen who quietly, and sometimes not so quietly, ran the city. That's where the action used to be, on the Hill.

But things have changed. If you want something done, particularly something that can make you money, the Hill can't help as much any more. More often you go to the District Building, and you want the skids greased so that you have quick access to the people you need. You take a genuine and sincere interest in who becomes mayor. You become civic-minded, in a hurry.

The D.C. government can do more, for more people, than in the past. Take the area of development. A lot of the action for local developers used to be with agencies like the National Capital Planning Commission or the Pennsylvania Avenue Development Corporation. Now the role of those agencies has greatly diminished, while the largest ongoing construction project in town, the new D.C. Convention Center, which is supposed to catalyze a major flurry of development in a wide swath between Massachusetts and Pennsylvania Avenues, is being coordinated from the District Building. Mayoral appointees dominate the Redevelopment Land Agency, which is responsible for the disposition of building sites downtown, considered the D.C. version of the Mother Lode. The mayor, through his agent for historic preservation, has life-or-death power over many older buildings, and must be dealt with by any developer who wants to tear one of them down.

The city rents property, sells property, seizes property, zones property, taxes property, closes alleys, upgrades streets or lets them decay, and in general can make a developer or break one. This may explain why said developers have been eager to give money to anyone with the remote chance of becoming mayor.

For example, before last Jan. 31, developers, investors and architects interested in just a single project -- the Portal tract in Southwest, which the Redevelopment Land Agency was about to allocate for development -- gave $15,000 to Barry's campaign. That was nine months before the Democratic primary, but none too soon, it seems, for those who wanted the rights to build on the Portal site.

Or take the area of finance. The city used to keep its money in the U.S. Treasury; now it keeps its ready cash -- millions of dollars -- in local banks. The mayor has already taken in thousands of dollars from local bankers and their spouses. However, it's not always easy to tell just what these bankers are interested in, since many are involved in development and other kinds of deals with the city as well.

Congress no longer dominates the day-to-day affairs of the city. The District Building lets its own contracts, sets its own tax rates, writes its own land-use laws, and, in general, behaves like an ordinary metropolis.

The D.C. government has also moved into entirely new areas that Congress never got a chance to deal with. For instance, at some point during the next mayor's term the city will let a franchise to a cable television operator. Sure enough, Barry reports a $2,000 contribution from a cable television operator who is known to be most interested in that franchise.

This is all old hat in most other cities, and in fact amplifies an established trend here in Washington. There were contributions from bankers and developers last time around, too. But never before have the city's rich and famous, and those who merely aspire to that status, been so deep of pocket -- and this during a recession to which the white-wine crowd has not been immune.