ONCE MORE into the sludge. This time the question is whether sewage sludge can be used as a building material. It sounds unlikely, but that's roughly what officials in Montgomery and Prince George's counties are trying to work out right now. Montgomery, you see, faces a development freeze unless it can find more sewage-treatment capacity. Prince George's has capacity to spare, but would love to have its sludge composted somewhere else-for instance, in the rural reaches of Montgomery. And the obvious trade-off has an extra benefit. Besides getting the sludge out of Prince George's and allowing building in Montgomery to proceed, a joint composting facility could save the two counties $40 million or more.

If this is good bargain, which he think it is, why wasn't it arrived at years ago? Three things have changed. Montgomery has become more interested in economic development. Growth in Prince George's has slowed down. Most important, both counties have acquaried new leaders who want to overcome old hostilities and settle the tedious "sewer wars." True, Montgomery County executive Charles Gilchrist and his chief administrator, Robert Wilson, are proceeding warily; Prince George's executive Larry Hogan who enjoys the advantage, is likely to be tough. Still, the sludge-for-sewage concept seems to be gaining more support by the day.

The Rockville-Upper Marlboro axis is not the only track on which discussions have started afresh. District Mayor Barry is talking with everyone. The city, too, wants more Blue Plains capacity to accommodate development. It also wants to export its own sludge, and is now trying to persuade Virginia to tolerate a processing plant in King George County downriver.

What's happening, in short, is that new leaders are taking new looks at old problems and trying to bring regional arrangements into line with current needs and patterns of growth. Moreover, they all seem interested in staying out of court-and in touch with the federal officials who will have to approve each accord. Solutions may come slowly. Still, the atmosphere is as promising as any we recall since the region's governments started arguing over sewage and sludge-which was at least half an oen ago.