THETIS ISLAND, British Columbia- Donovan Saul shuffles down the road, his eyes glued to the ground. Suddenly, he jackknifes and scoops up from the roadside what appears to be a gobbet of Silly Putty.

The thing bangs limply on Mr. Saul's glove for a moment and then plops into a pail, joining a bunch of other pale, shapeless things slithering around in their own slime.

Mr. Saul makes his living as a professional slug catcher. He sells them for $30 per hundred slugs, and most of his customers are biology teachers with plans to dissect. Each year his one-man company. Beaver Biological Supplies, ships thousands of the slimy creatures all over the world from this damp little coastal island. Only about 200 people live here, but there are tens of thousands of fine, fat slugs. some measuring a foot in length. Mr. Saul proudly compares Thetis Island and its slugs to Bordeaux and its wines. "You can't find slugs as big or as plentiful anywhere else," he boasts.

There is one big open question: Why should anyone want them? The humble slug, a gastropod land mollusk (genus Limax) is no beauty. A relative of the snail. it is spurned by the squeamish and hated by gardeners the world over. It can eat its weight in vegetables in one sitting, making good use of its 3.000 tiny teeth. How much demand, after all, can there be for a repellent little animal with four noses that prefers to live under a rock?

Plenty, actually. Allen Gelperin, a neuroscientist at AT&T's Bell Laboratories in Murray Hill, N.J., heads a team of researchers who hope slugs can help them develop computerized artificial intelligence. Half a dozen other labs in the U.S. and Japan are trying to do the same thing, he says.

Slugs, it seems, have an unusually well-developed sense of smell. Mr. Gelperin and his Bell Labs cronies have managed to find the link between a slug's nose and the olfactory receptor part of its brain. "We puff odors on the nose cells and watch to see how the brain oscillates and changes," he says. Carrot and mushroom smells seem to trigger the most reaction.

The Bell Labs team has trained slugs to shun their favorite foods by pairing such odors with tastes slugs seem to hate-quinine, for instance. The scientists hope eventually to map the slug's neural transmission patterns and use the information thus gleaned to develop computer software that can read stimuli much the way a police scanner reads radio signals.

"The advantage of the slug," says Mr. Gelperin, "is that it is complicated enough to be interesting, but not so complicated as to be intractable."

Ms. Deyrup-Olsen has a researcher's interest in the slug's amazing ability to produce mucus. When alarmed, a slug can secrete one-third its body weight in mucus, a substance that feels a bit like Krazy Glue and Is next to impossible to remove. Slugs use the stuff to grease their paths, exuding it from a gland beneath their heads and slithering along, leaving shiny slime trails in their wake. They can even sling the slime from trees and slide down, Tarzan style.

Ms. Deyrup-Olsen says the slugs' glands ooze mucus at will to protect their delicate skin. They will also slough their protective slime shield so as to remove bacteria and other contaminants. "Then they eat it." she says. (Table manners aren't the slug's strongest selling point).

But Ms. Deyrup-Olsen believes slugs are well worth having around. Indeed, their sliming mechanism could hold keys to understanding such diseases as cystic fibrosis-a fatal, congenital disease of children-and gastric ulcers. In both, the body fails to properly secrete a protective mucus shield.

Slugs' well-known penchant for beer is something else that fascinates researchers. Organic gardeners know to put out containers of beer for slugs and snails to climb into and perish. "People kept asking me which beer do they like best?" says Whitney Cranshaw, a biologist at Colorado State University. in Fort Collins. So, three years ago, Mr. Cranshaw conducted a taste test that might have pleased Anheuser-Busch Cos., but probably didn't.

He rounded up 2,500-odd slugs and put out 16 brands of beer in saucers. Budweiser was the slugs' favorite, 5-to-I, according to Cranshaw's paper on the project. The winners, as does happen, died in their beer. Anheuser-Busch hasn't used the research findings in its advertising. Spuds Mackenzie being a more effective spokes-animal for Bud Light than a suicidal, alcoholic, hermaphroditic, slug could be.

The University of California at Santa Cruz, on the other hand, has chosen the slug as its mascot, The school's 9,600 students voted overwhelmingly in 1986 to replace the sea lion with the slug,

Santa Cruz went a little nuts at first over its new mascot. "The basketball team started wearing those boing-boing antennae and creeping out on the floor on their bellies, making cellophane slime trails," says Daniel Wood, the school's sports director. Opponents still occasionally show up hearing giant salt shakers (salt makes slugs shrivel up and die a horrible death by dehydration). But the Santa Cruz Slugs get fewer taunts these days. "Athletes kind of like the slug's status as perpetual underdog," says Mr. Wood.

Indeed, slugs do seem to arouse mixed emotions, especially here in the Pacific Northwest where they abound as nowhere else: There are said to be more than 600 of them hanging out in the average garden. EM. Matson Co., a Seattle concern that sells tons of an ominously named pesticide called "Corry's Slug and Snail Death" also does a brisk business in T-shirts that feature a couple of likable slugs peering from a box of slug halt.

Theodore Roethke, the Northwest poet, once composed a paean to the slug. The late Mr. Roethke called the creature a "loose toe from the old life" and compared its "white skein of spittle" to quicksilver .."beautitul, in its way,"

Up and down the Pacific coast, small towns exploit their slugs by holding annual slug derbies. (A very fleet slug can cover 50 yards in a day-no snail's pace-though most races are held, for the sake of expedience, on a one-yard course).

At the annual Slugfest in Guerneville, Calif., the main attraction is a bakeoff. with a panel of judges gamely eating their way through slug specialties supplied by local residents. If snails are a delicacy, why not slugs? A sampling of this year's entries: sweet and sour slugs and slug pizza. A martini, with a slug instead of an olive (and, of course, a slug of gin) tastes "just awful," according to Sonoma County Sheriff Richard Michaelson, a member of the judging panel.

On Thetis Island. Mr. Saul is himself ambivalent about slugs. He dispatches more than his share: Piles of five-gallon buckets brimming with dead slugs pickling In formaldehyde line his laboratory, and that's just a two-day catch. But since he bought Beaver Biological four years ago and left his job as a wildlife ranger, he says he's come to identify with his prey.

At the island firehouse, chums of Mr. Saul refer to the 35-year-old biotechnologist as "Slug Man." And he readily admits to certain humane impulses: "I'm probably the only one on the island," he says, "who swerves away when he sees a slug on the road."