IT IS A COLD fact of colonial life that the extent to which residents of the District of Columbia may govern themselves is ever precarious--because what Congress gives, Congress can take away. Just like that. The local government and, as people have been bluntly reminded this week, the local system of justice exist merely at the pleasure of Capitol Hill. That's the message underscored by a bill introduced by Maryland Sen. Charles McC. Mathias Jr. that would bring back the days of strict White House control over D.C. courts as well as city courtrooms ruled by judges who live in the suburbs.

Mr. Mathias, it should be noted, was a principal author of the current D.C. charter provisions that allow the city some reasonable role in the selection of its local judges. The senator notes that he introduced the measure at the request of the Reagan administration, in his capacity as chairman of the Senate subcommittee that still oversees District legislation. The bill is merely a vehicle for re-examining current procedures, which probably could stand some "fine-tuning," Mr. Mathias says, and is not necessarily a plan he will ultimately embrace.

We should hope not. It would be the sharpest blow to local self-government in years, a stunning reversal of the important progress for home rule that began in the Nixon years and has been built upon ever since.

Besides, the current system is hardly a total abdication of federal influence on local justice here: under the charter, a seven-member commission sends the White House a list of three candidates-- residents of the District--for any vacant D.C. judgeship. The president has 60 days to choose one for Senate confirmation, or else the commission may make make its own nomination.

But the measure introduced by Mr. Mathias would undo his own original good work: there would be no time limit for presidential action. The president could keep asking for more names indefinitely--and could pick any member of the D.C. Bar who lived within 20 miles of the District to be a judge. And if a president didn't care for the membership of the nominating commission, he could change that at will.

Are residents and elected officials of the District incapable of selecting competent judges for their local courts? Of course not, and if Sen. Mathias still believes in the rightness of local self-government in the District of Columbia, he should withdraw this proposal in favor of constructive changes--such as letting the mayor nominate D.C. judges who would serve as well as live in the District.