Making a loud four-letter suggestion to a police chief may be dumb and is most surely indiscreet, but the U.S. Supreme Court agreed in a Maryland case yesterday that the word used in the suggestion is neither obscene nor profane.

The high court, without comment, refused to reinstate a Hancock man's conviction for disorderly conduct after he allegedly shouted the vulgarism on the night of Jan. 8, 1980, at Vincent Gavin, then the Western Maryland town's police chief. Robert Diehl, the central figure in the case, was a passenger in a car stopped by Gavin.

According to lower court records, Gavin said Diehl stepped out of the car and was told to get back in, whereupon Diehl said the word that provoked the charge and another of resisting arrest. Diehl was convicted of both.

Maryland's highest court, the Court of Appeals, overturned the convictions last October on the grounds that the word in question was not "profane" because it wasn't religiously irreverent and not "obscene" because it wasn't erotic. State lawyers had contended the use of "fighting words" should sustain convictions.

For Diehl, the high court action is, at least to a degree, academic. He's serving time in a state prison at Hagerstown on an unrelated conviction. And ex-chief Gavin, saying he's "kind of happy I got out of law enforcement," now teaches social studies at Hancock High School.