THE OPERATIONS of the District of Columbia provide a fertile field for congressional hearings, especially, it turns out, in even- numbered years. It can always be argued, after all, that Congress has a "responsibility" to oversee things here, home rule or not. So it is that, even though this city enacted important legislation just last year to tighten local controls on cabs, Maryland Rep. Michael D. Barnes the other day called a hearing on the "quality and reliability of taxicab service."

That's a hot enough topic, for sure. There's hardly anyone around who hasn't had some awful emotional experience with cabs here: rejection, insult, desertion or the urban equivalent of highway robbery. It's true, too, that Mr. Barnes is chairman of the House District subcommittee on government operations and metropolitan affairs. Far less clear, though, is what the hearing accomplished that hasn't, shouldn't or couldn't have been duly handled by the city government, which is responsible for regulating cab service.

Mr. Barnes concluded -- listen to this -- that better regulation of the taxis is needed "and long overdue." Rep. Stan Parris of Virginia got an opportunity to speak out about charges of extortion and kickbacks in cab safety inspection operations -- which the city government has been investigating.

Certainly there's plenty of investigating and regulating for the city government to do as it tests the new laws it has enacted. That's where the responsibility should be under home rule too. Congress supposedly unburdened itself of this kind of local business. Or did it?