LIKE A REBELLIOUS adolescent, Fairfax City has been kicking up a fuss over its relationship with Fairfax County and the rest of the region, threatening to go it alone in providing local services - however maladroitly. As you may have read, one of the latest battles has been over public transportation. The city leaders' insular thinking has led them to pick up their metro marbles and go home to a plan for their own chartened commuter bus service beginning Tuesday.

There are certain decisions, of course, that your block club, neighborhood or city ought to be able to make by itself. But any thoughtful government leader hereabouts realizes that the carefully nurtured regional approach to mass transportation - complex and expensive though it has become - is the only sensible way to go. Fairfax City leaders, however, are content to take care of their rush-hour commuters to and from Washington and never mind any other transportation needs of people. Those needs, they argue, can be taken care of somehow by other bus lines, including Metro. In other words, they want to use the best of the Metro lines and have no part of its costlier but necessary routes.

It turns out that Metro leaders aren't so sure they want to continue running eight of the other bus routes that link the city with the county; and they're considering dropping some of the existing services and not stopping any buses in the city to pick up or discharge passengers. If Fairfax City doesn't want to participate in Metro, why should Metro keep serving the city?

The city government's isolationism hasn't been confined to bus service, either. The city and the county have been battling over the costs of services that the county provides. On Dec. 12, John F. Herrity, chairman of the county's board of supervisors, informed the city that if there is no agreement on new contract terms by March 1, the county will start charging higher costs and "should the city fail to pay promptly as billed, all such services to the city will be terminated." Mr. Herrity also has said that, barring an agreement on school services (which are mostly in the form of county teachers working in the city schools), they would be discontinued on July 1, 1979. City Attorney John H. Rust Jr. claims the county can't do any of this. Meanwhile, the city already has decided to take over the fire and rescue service that the county has been providing.

When will the residents of Fairfax City realize that the provincial antics of their local leaders are neither realistic nor constructive?