Wasington portrait artist Charles Merrill Mount lost another lawsuit when a federal judge last week dismissed a $100,000 action Mount had filed against his Arlington landlord.

Mount, 50, claimed in the suit that Army Capt. William English had failed to tell him that Interstate Rte. 66 was going to be constructed near the house that the officer rented the artist. Workers began clearing land adjacent to Mount's home five months after he moved in two years ago.

U.S. District Judge Albert V. Bryan Jr. dismissed the suit against English because federal marshals had failed to locate English and serve him with a copy of the lawsuit.

The lawsuit Mount brought against his landlord is but one in a series of legal actions in which the painter is currently involved.

Two months before Mount filed his suit, English sued the painter for back rent on the Arlington house. An Arlington judge, William Corman, last month ordered Mount to pay nine months' back rent and court costs in that action.

Warren W. McLain, English's attorney, said yesterday that Mount has not paid. In fact, Mount has filed a motion in Arlington Circuit Court to overturn the judgment. "Once the suit against Judge Corman is disposed of, I'm going to try and collect the best way I can," said McLain.

The most celebrated and convoluted of Mount's legal wranglings, however, involve portraits he painted of former Mississippi senator James O. Eastland. Mount charges he was cheated out of $13,400 in fees owed him for works he completed in connection with the portraits.

He sued the University of Mississippi Foundation for the fees in federal court but the suit was dismissed on procedural grounds. Mount filed another suit earlier this month against the university, adding former Senate Judiciary Committee staffer Francis Rosenberger to the defendants, and asked for $500,000 in damages.

Mount calls that suit a "civil rights" case. "Artist," he charged in an interview yesterday, "are considered third-class citizens. I intend to change all that."