Asserting that the region is unable to cope with its mounting output of sewage sludge, officials of the District, suburban Maryland and Fairfax County have told the federal government that they can't go forward with their promised improvement of the big Blue Plains treatment plant.

Without the improvement, the region will not be able to carry out its pledge -- backed by hundreds of millions of dollars of federal aid already spent -- to make the Potomac River a major urban recreational resource.

The equipment for the improvement -- an elaborate series of filters -- should be ready for use in late summer or early fall. But the filters will treat 700 tons of sludge a day -- and that enormous residue, local officials say, is the reason for the dilemma.

Blue Plains already produces about 1,200 tons of sludge daily from other treatment processes. Most of the sludge is buried in trenches or vacant land in Montgomery and Prince George's counties. But land is in short supply and is expensive. Counting trenching, landfilling and composting, the area spends more than $17 million annually to dispose of Blue Plains sludge.

Earlier this week, a meeting was held of the chief administrative officers of the localities using Blue Plains -- Elijah B. Rogers of the District, Robert Wilson of Montgomery, Kenneth V. Duncan of Prince George's and J. Hamilton Lambert of Fairfax. They decided that there was no practical way to dispose of any more sludge.