THE POSTAL SERVICE has the perfect answer to the budget cuts that were imposed on it last year. Since it has its own revenue source and essentially pays its own way, it wants to be taken off budget. If it doesn't show up in the federal accounts, it can't be a target in the efforts to balance them: that's the idea. Postal officials are already pushing for a bill. Color us invisible, they're urging Congress.

Some members of the authorizing committees are disposed to go along. Their reasons are partly self-protective. The Postal Service is a zero-sum game. To constrain its budget means to say no to the powerful postal unions (there are 800,000 postal employees) or major users or the public at large or all three, and what fun is that? Defenders will also argue that, for all the horror stories always in circulation, the mostly independent service is on balance performing reasonably well and shouldn't be subject to the game of crack-the-whip that is played with the larger federal budget each year.

Maybe not, but this bill is the wrong way to shield either the service or Congress. The service was transformed from an old and slightly disreputable federal department into a quasi-independent agency in 1970. Partly this was done because Congress was tired then, too, of apportioning disappointment in the filling of postmasterships and of taking the heat for the quality of service and the price of a stamp. As befitted an agency born in a Republican administration, the sleek new service was to be run with the efficiency of a private corporation, and to some extent it has been run that way. Now the proposal is to free it even more.

But the pretense that this is a private enterprise can only be carried so far. It's a federal activity, publicly financed, a power of Congress in the Constitution ahead even of creating courts and declaring war and maintaining a navy -- "To Establish Post Offices and Post Roads." The budget is meant to reflect the full range of federal financial activity so that, in its impact on the economy, this activity can be both appreciated and controlled. Congress can't -- or shouldn't -- turn a blind eye to the revenues and spending of the Postal Service, hitched as it is to its own money machine, any more than it should to the Veterans Administration or the Agriculture Department (both of which are much smaller).

The "postal community," as it is sometimes oddly called, is not alone in seeking exemption from what discipline survives in the federal budget. Thus the Social Security trust funds have now been declared "off budget," an effort to insulate them from the unpleasantness of deficit reduction, and similar status has been sought, so far unsuccessfully, for the highway and airport and airways trust funds, each with its own tax.

This fragmentation of government is a bad idea, and nowhere more so than when it affects the broad unifying domestic services that the government performs everywhere at the same average cost. The delivery of the mail is one of those. Congress should accept the responsibility it retains for this and keep it in full view in the budget, where it belongs.