Prince George's County has filed suit against suburban Maryland's water and sewer authority in an attempt to block construction of a $4.5 million sludge composting facility in neighboring Montgomery County.

The action against the Washington Suburban Sanitary Commission, which serves both counties, could jeopardize a widely hailed regional agreement designed to head off a sewer moratorium that would slow or halt development in Montgomery County and the District of Columbia.

The critical final element of the agreement requires the two Maryland counties, the District of Columbia, and Fairfax County in Virginia to submit long-range plans for disposing of the 1,200 tons of sludge produced daily at the Blue Plains regional treatment plant in D.C. U.S. District Judge John Lewis Smith Jr., who has arbitrated the region's protracted sewer wars in the 1970s, has set Jan. 1, 1980, as the deadline for filing the plans in federal court.

But the suit filed Nov. 27 by Prince George's County in the county's circuit Court could upset Montgomery's contribution to the long-range plan.

Montgomery had hoped to convert its share of sludge, which is the residue of waste water treatment, into soil conditioner at the proposed composting facility near Calverton in the Rte. 29 corridor about two miles from the Prince George's County boundary.

Prince George's County leaders long have fought the proposed composting facility, contending it could produce an airborne fungus that would endanger the health of 25,000 nearby residents. They also argued the trucks going to and from the facility would create severe traffic congestion in the area.

They lost their fight in Judge Smith's courtroom and before the state health department and a state review board. The suit, confined to technical objections to the sanitary commission's plan for land acquisition and construction, marks yet another attempt to stop the composting plan.

Nathan J. Greenbaum, assistant county attorney for Montgomery, said if the suit succeeds, "I don't know where the county will put its sludge. We don't have an alternate long-range plan."

Most sludge from the Blue Plains plant currently is being buried in trenches in Montgomery and Prince George's but there is general agreement that space will not be available indefinitely for that purpose.

Montgomery County is not alone in encountering difficulty trying to build a composting facility. The District of Columbia had to abandon plans to build one on unused parkland in Oxon Cove near several residential neighborhoods. A private company, Dano, wants to convert all of Blue Plains' sludge and D.C.'s trash to compost, but has failed to get a site in Prince William, Stafford and King George counties in Virginia.

The only functioning composting facilities are a small experimental one at the U.S. Agriculture Department's Beltsville research facility and a slightly larger one at Blue Plains.