The Monster of the Potomac - or Chesapeake Chessie, depending on who claims to have seen what, and where - shows little sign of being verifiable scientifically, although it may become viable commercially.

Despite wide coverage last week of reports that a 25- to 30-foot serpentlike creature was seen in the lower Potomac River, no new sightings have been reported. For many people enchanted at the idea of a real monster in the river, that was bad news.

John Merriner, head of the ichthyology division of the Virginia Institute of Marine Science, said, "We would be delighted to find out what this thing is, if it is a new animal. But in view of the amount of activity on the bay, historically and presently, it is unlikely that there would be something undescribed or unknown."

He asked that anyone sighting a creature attemtp to photograph it and take careful notes on such data as time, distance, size, movement, color, depth and location of the sun.

And, he said, don't shoot at it, as did one witness at an earlier sighting. "If it is a giant animal, it might be injured, get mad and attack someone," Merriner said. "And if it is unique, it is less valuable to science if it is dead."

A spokesman for the Fund for Animals, an animal protection organization, gave another reason not to shoot. If the monster turns out to be a dolphin, porpoise or whale, the maximum penalty for killing it is a $20,000 fine and one year in jail.

New accounts of sightings prompted calls and letters about previous sightings, but most did not resemble descriptions given by groups of people in Northumberland County who reported three separate sightings in June and July. No one has seen the beast more than once.

There was one report of hugh "reptilian" footprints on a beach near Leonardtown, Md., and some accounts soon said the creature looked exactly like the Loch Ness Monster.

Bruce Hickman of Mitchellville, Md., reported a May sighting at Calvert Cliffs. His "Chesapeake Chessie" was chasing a school of fish at high speed, kicking up a large wake but not showing above water.

Craig Phillips, one of several marine life authorities who have taken an interest in the reports, suggested that the creature might have been several bottle-nosed dolphin swimming in line, a large snake let loose from a collection or a log.

Phillips, director of the national Aquarium, said a snake would travel at night and hug the bank. Any large animal such as a shark, whale or otter could create a wake that appears to be undulation, he said.

Waves washing over a pole or log also could create the illusion of a creature undulating through the water, he said.