LOCH NESS, SCOTLAND, OCT. 11 -- It looked like a chicken scratch, or perhaps a pencil mark drawn by a particularly unsteady two-year-old.

But to those with trained eyes, the thin, shaky line on the paper was the sonar signature of something big and alive, moving slowly about 600 feet down, deeper than any proven large life form in the chill, murky waters of this mysterious Scottish lake.

No one here was prepared to say that it was the Loch Ness Monster. But few would swear it wasn't.

For the past three days, 20 cabin cruisers have been sweeping Loch Ness with underwater sound in the most ambitious, and certainly the most expensive, expedition ever launched to find the elusive "Nessie," the legendary creature of the deep first reported to have surfaced here more than 1,400 years ago.

That first sighting was made by St. Columba, the missionary who spread Christian doctrine through northern Scotland. Hundreds, perhaps thousands, have claimed to have seen Nessie since, including many of the current residents along the lake, or loch, in the Gaelic language. Most describe it as looking like what scientists have identified as a plesiosaur, a predatory reptile with a tiny head and long neck, atop a massive, four-finned body, last known to have lived 70 million years ago.

This weekend's scan was one of the more serious of a decades-long series of attempts to catch the wily creature, from scattering breadcrumbs along the surface of the lake, to playing its favorite songs on a lakeside piano.

Lined up port to starboard across the mile-wide lake, the boats moved in a line up and down its 23-mile length, bouncing sound waves from the surface down to its 720-feet-deep bottom, hoping to intercept something in between. Each underwater "contact" was electronically transmitted to a shipboard computer, which scratched its message out with a needle on a roll of paper read like an electrocardiogram.

Three days worth of paper rolls turned up conspicuously empty, except for densely packed dots along the top, most of them denoting "I had a tendency not to believe in monsters even before I came here. I would tend to want to think it's a seal."

-- Darrell Lowrance

salmon living close to the surface. In all, there were only three of what expedition leader Adrian Shine, 38, called "genuine deep water contacts;" three small markings on the rest of the otherwise blank paper. Only one of the three, Shine said, the wobbly little scratch resembling a spread-eagled, upside-down letter "V," was definite enough to be worth getting excited about.

Shine, a serious man with an intense, icy stare and a full-flowing beard, maintained from the start that he did not believe in the monster. An amateur scientist who works for a printing company, he has spent most of his spare time for the past 15 years staring into the peat-stained depths of Loch Ness and other nearby lakes, searching for a way to explain mysterious phenomena like Nessie.

The expedition findings, he said, echoed those of his 1982 exploration, a less ambitious sonar sweep that also made deep water contact. Such a creature, he said, was explainable by known, natural phenomena. "There is no reason why there shouldn't be something at the top of the food chain here," he said at a news conference last night. "There is nothing outrageous about a large fish predator.

"You want me to deliver a monster . . . a media monster," Shine said somewhat petulantly to the more than 200 reporters who gathered here for his expedition. Centuries of reported sightings may have been "enough to impress local witnesses," he said, "but they're not enough to create a Jurassic reptile."

Darrell Lowrance, whose Tulsa, Okla.-based company provided the sonar equipment, noted apologetically that he was "a doubter to begin with. I had a tendency not to believe in monsters even before I came here." As for the deep water contacts, Lowrance said, "I would tend to want to think it's a seal."

Most people who find it hard to believe in the monster, but do not dispute that something is there, believe it could be a sea seal, who enters the lake through the River Ness, at nearby Inverness, or a large eel. Those who do believe in Nessie explain that a family of the creatures could have gotten trapped inside the loch, part of a deep trench cut northeast to southwest across Scotland during the last Ice Age, when the prehistoric sea receded and cut it off.

One of the most ardent believers is Ronald Bremner, owner of The Clansman Hotel, where the expedition was headquartered, and founder of the Official Loch Ness Visitors Center in the nearby town of Drumnadrochit. "I disagree with Adrian {Shine} in that I'm not totally convinced it's a big fish or an eel," Bremner said. "Because I've seen it."

Shine noted that the expedition did confirm some newly discovered forms of life in the lake, including vast layers of small fish that rise and fall in layers as the surface water heats and cools. "I'm sure you're not very interested in what the Americans would call bait fish," he sighed.

But without the media monster, Shine knows, there would be no money to fund his explorations and those of dozens of others who over the years have come here to look for whatever it is that may live in Loch Ness. Lowrance, one of the principal sponsors of this weekend's search, surely did not mind the reporters.

Press invitations to "Operation Deep Scan," as a public relations firm hired for the exercise dubbed the search, went out all over the world months ago, along with plane tickets and lodgings for those who would accept them. No one involved would put a total price on the expedition, except to say that the loaned equipment, including local boats, was worth an estimated $1 million.

Media madness has long surrounded the search for Nessie, ever since a series of alleged photographs of the monster were first taken in 1933, the year the first paved highway was constructed along the northern lakeside. Nearly all of the photographs have been discounted as inconclusive, or even fakes. One of the earliest publicized claims, based on massive footprints found along the shore, turned out to be a hoax perpetrated with the aid of an umbrella stand made from a hippopotamus foot.

Although there remain a few unexplained bits of alleged evidence of Nessie's existence, the hardest proof to dismiss has been the eyewitness accounts of an average 20 people a year. Most have been locals, who say that, despite the estimated $225 million in tourist dollars that Nessie brings here each year, they would just as soon be left in peace with their monster.

There is very little development along the remote lake, nary a Monster Burger stand in sight and only the Drumnadrochit center to cater to outside Nessie-seekers. So protective are the residents of this pristine land and the lovely lake that holds the largest amount of fresh water in all of mainland Britain, that they are taking the local government to court for giving planning permission to Loch Ness' first industry: a proposed fish farm.

Many of them won't even talk about their sightings. But some, including elderly lakeside resident Donald Mackinnon, have been persuaded to record their experience for posterity and the Official Visitors Center.

"It was in the winter of 1970," Mackinnon said. "Then I saw it . . . the monster coming across . . . the long neck about six feet long. And you could see two humps. The beast itself, it would have been about 30 or 40 feet long." After he and a companion stood and stared for about 10 minutes, Mackinnon said, "it just went down, like a submarine."