TO THE PREDICTABLE distress of its beneficiaries, the nation's $400-million-a-year program of federal "impact aid" subsidies to public schools attended by children of federal and military employees has been all but eliminated in the budget President Carter sent to Congress this week. If this decision were to stick, schools in Greater Washington would stand to lose more than $28 million - with Fairfax County taking the greatest local loss, at $10.6 million. We say "if" because this is an old fiscal story around the White House and Capitol Hill: Presidents Nixon and Ford both sought to eliminate these funds, only to be overridden by the Democratic-controlled Congress; indeed, it's been one way that Presidents could trim their budgets and let Congress put the program back anyway.

Sure enough, Rep. Herbert E. Harris (D-Va.), who had asked Mr. Carter to support the program after its last rejection by Mr. Ford, is already working to organize a bloc in the House to challenge this latest decision. He is quick to note that failure to obtain the federal money would mean cutbacks of school programs or increased local taxes. In Fairfax County, the congressman points out, each property tax bill would have to be raised by $68 to offset the impact aid curtailment.

That's an impact, all right - but the whole impact-aid program has built-in flaws in the first place. Under this roundabout way of packaging and distributing federal support for public schools around the country, some of the nation's most affluent suburbs - which include those ringing this city - have been doubly endowed by having residents who are relatively well paid federal workers. The program subsidizes children whose parents work on federal property, which in this area means money for suburban school districts to cover residents who, for the most part, work in the city. In effect, then, you have Mr. Harris - one of the most vocal opponents of city tax on suburban residents - pleading to retain what amounts to a reverse-commuter-tax plan.

Under the Ford administration proposal, now embraced by Mr. Carter, the federal government would continue to subsidize only the education of students who actually live on government property or military bases, such as those who live at Ft. Belvoir or Andrews Air Force Base in this region. Certainly there is more logic to a program for those circumstances than for a wide-open "impacted-area" system of nationwide grants.

Still, a sudden and total elimination of the other impact aid program would pose severe problems for a number of school districts here and elsewhere. It may well be that a phased shutdown of the program would ease the impact on local budgets. But rather than continuing the annual resuscitation of a politically attractive though unfair school aid program, Congress should examine other ways to compensate for unusual burdens of the federal presence, such as untaxed federal land.