It was a bad day for Prince George's County in the sewer wars. It lost a skirmish on its western front.

In a rare confrontation between federal and state courts, a U.S. judge yesterday ordered the Washington Suburban Sanitary Commission to ignore a Prince George's County judge's injunction halting construction of a sewage-sludge composting facility in Montgomery County near Prince George's western edge.

One root of the county's wars with its neighbors over who gets the sludge is Prince George's contention that it has been ganged up on by the other localities, especially its more affluent neighbor, Montgomery. The county wants the plant built farther inside Montgomery.

U.S. District Judge John Lewis Smith Jr., obviously annoyed that a series of his orders have been held up by suits filed in Prince George's courts, told the WSSC (suburban Maryland's water and sewer agency) to build the Montgomery sludge composting facility "at the earliest practicable date."

The long-planned, $34 million plant, which Montgomery says it desperately needs to dispose of its mounting share of regional sewage sludge, would be built in the Rte. 29 corridor about a mile from the Prince George's line and near the Calverton community that straddles the boundary.

Despite improved technology to eliminate odors and possible environmental hazards, sludge composting plants still set off nervous jitters in neighborhoods that would be near them.

In a big victory for Prince George's -- and the Calverton Citizens Association -- just 11 days ago, county Circuit Court Judge Robert J. Woods issued an injunction forbidding the WSSC from acquiring so-callewd Site 2 in Montgomery and building the composting plant. Woods ordered the case to go to trial in August.

But now that trial -- along with the June 17 injunction -- has been mooted by U.S. Judge Smith.

Ordinarily, Smith, who has been refereeing the sewer wars for seven years, is a model of equanimity and forebearance. Yesterday he sounded as if he had had enough.

After reading excerpts of the judge's order, Aaron Handleman, attorney for the Calverton Citizens Association, stood up and said, "Your honor, may I ask for a clarification?"

"No clarification is necessary," Smith said. Then he rose from the bench and left the courtroom, while Handleman and Prince George's County Attorney Robert B. Ostrom soaked in the impact of what many legal observers said was an extraordinary decision.

"It is a significant step for a federal court to stop parties from enforcing a state court order," said Montgomery Assistant County Attorney Nathan J. Greenbaum. "It's unusual and done in only rare circumstances."

The state courts and their federal counterparts, are, under the U.S. Constitution, separate systems. Prince George's has maintained that the issues before Circuit Court Judge Woods were state matters -- out of Judge Smith's jurisdiction.

After Smith yesterday rejected that argument, Ostrom, said, "I'm discouraged, but to say I'm surprised by his (Smith's) decree would not be candid."

At yesterday's hearing, Prince George's was a minority of one. Lined up against the county were Montgomery, the WSSC, the U.S. Justice Department (representing the Environmental Protection Agency) and the states of Maryland and Virginia.

Said Maryland Assistant Attorney General Ben M. Bialek before Judge Smith: "The state looks with dismay at what appears to be court shopping by Prince George's."