The National Capital Planning Commission yesterday pleaded with Arlington to turn down the lights.

The planning agency unanimously urged the county not to permit MCI Communications Corp. to erect large orange lighted roof-top signs on buldings it is leasing south of the Pentagon. The signs, the planning agency said, would be clearly visible from Arlington National Cemetery, the George Washington Memorial Parkway and the Mall.

Architect Joel Redick told the planning agency that MCI is a young, expanding company that needs the signs as "a natural design way of saying we're here."

The Arlington County Board, which a year ago approved controversial roof-top signs on the USA Today building in Rosslyn, will vote tomorrow on a request by the MCI to place up to 12 lighted orange signs, each 8 by 22 feet, on the roof of two new 12-story office buildings in Pentagon City.

The county's planning staff opposes nine of the MCI rooftop signs, because they would be visible and possibly annoy residents in nearby Arlington Ridge and Aurora Hills neighborhoods. It supports three signs facing Northeast, Northwest and Southeast which would be visible from I-395, the parkway, and parts of Arlington Cemetery and the Mall.

The Army, which operates Arlington Cemetery, has strongly opposed any lighted advertising signs visible from the cemetery. The MCI signs would be "a visual intrustion . . . on this national shrine" and should not be approved, William McCormick Jr., spokesman for the Army Corps of Engineers wrote the planning commission last week.

A proposed USA Today sign facing the cemetery was rejected by the Arlington board, but the board approved a lighted sign facing the Kennedy Center and Georgetown, also partially visible from the Lincoln Memorial.

The federal planning commission, which has unsuccessfully challenged Arlington's approval of high rise construction and signs that are visible from Washington, has no jurisdiction over private land in Arlington.

In yesterday's action, the federal planning agency urged the county not to permit any rooftop MCI signs facing north, northwest or northeast. However, it said if the county board insists on a building sign it should be a single, smaller, more subdued, Northeast sign and be placed below the 12-story roof level.

Rudick agreed that "you've got quite a problem" in Arlington with the growing profusion of high-rise buildings visible from the Mall and cemetery. The cemetery "is no longer a restful, peaceful place," he said, because there already is "a wall of existing buildings around it."