FOR NOW, AT LEAST, it doesn't matter what you may think about the merits of taxing unincorporated professionals from the suburbs who make their living in the District. In blunt terms, the D.C. Court of Appeals has spelled out the reason this tax can't fly, and it has nothing to do with anything any other city might confront. Congress, which dispenses and disposes any blessings of self-government, wrote a hooker into the "home rule" act of 1973: it's all right for the District to elect a government and enact local laws that don't make Congress mad -- but do not touch "any portion of the personal income" of commuters.

The professional tax was a nice try, but no soap -- the court pointed to all sorts of unfortunate legislative history behind the congressional act, including a statement by Sen. Thomas F. Eagleton (D-Mo.) during Senate hearings on the bill in answer to a question about the "commuter" tax: "Yes. There is a specific prohibition as to the imposition of a commuter tax, a reciprocal income tax, or any other tax on non-residents of the District of Columbia." No matter that many other cities around the country collect payroll taxes from out-of-state residents.

The court did cite one bit of congressional reasoning for the tax ban that District residents will find singularly unsound.During the Senate consideration, the opinion notes, Maryland's Sen. Charles McC. Mathias Jr. "elucidated the rationale for enacting the prohibition. . . . 'The increased federal payment also compensates for the Congress' refusal to permit the District to levy taxes on the income of non-residents.'"

That's been some dandy "increase" in the federal payment: in 1975, the payment amounted to about 25 percent of the local budget; but the last time anybody looked -- fiscal 1980 -- it was standing at about 17 percent. Sure, the dollar amount is up slightly; but so -- does anyone need to be reminded? -- is inflation. So, too, with this ruling, is the District's financial bind -- for the city faces a net loss of at least $41 million it has collected already and another $10 million or so that was expected to roll in this April.

Obviously some severe cuts in spending will have to be made -- and the sooner into the fiscal year, the easier they are to take. Mayor Barry says he recognizes the necessity of making these unpleasant decisions, and members of the council and the school board should face up to the task as well, without any unfair or irresponsible potshots. And until Congress is good enough to lift its colonial restraint on local taxing powers in the District, Sens. Eagleton and Mathias -- who in so many other ways have led the change for D.C. self-government -- might see what they can do about a more generous and equitable federal payment.