The man had no sooner finished bellyaching that there was nothing much to see on the day before the Montgomery County Fair officially opens when a chorus of bleating and splashing water drew his attention to something you don't see everyday: a sheep getting a bubble bath.

For the next half hour, he stood gaping with a dozen other onlookers as handler Susie Leib worked Orvus livestock shampoo into a foamy lather, then rinsed the Dorset yearling until her wool was white and fluffy.

"I really do like this sort of thing," the man confided, but added that he was disappointed that exhibitors hadn't yet set up more of their wares.

Today, when one of the largest agricultural fairs on the East Coast formally kicks off at the fairgrounds off I-270 in Gaithersburg, that won't be the case. For $1, $7 to $9 cheaper than it will cost for the rest of the seven-day run, fairgoers can see what has made the fair an attraction since a group of Montgomery County farmers first organized an exhibit of their best vegetables and livestock in Rockville in 1846.

There will be racing pigs and prancing horses, a magic show, music and the crowning of the 1987 Montgomery County Fair Queen. There will be demonstrations of churning butter and shearing sheep. The midway, with carnival games and breathtaking rides, will be in full swing. And the exhibitors, who have spent months and even years raising top-notch Jersey cows, 10-pound rabbits, beachball-sized squash, bright red tomatoes and brilliant purple and gold zinnias, will be on hand to see who will take home the first-place prizes.

For 141 years, including 39 years at the Gaithersburg site, the fair has stood as a testament to Montgomery County's agricultural roots. For a week each year, city slickers can marvel at the wonders of nature that their ancestors took for granted.

"Even though we have a lot of things to do in this area . . . people have a lot of respect for people who can still do things, grow things with their hands and can bring them up here and exhibit them," said Rose Ann Armes, who runs the flower exhibit and got involved with the fair as a 4-H Club member 15 years ago.

Yesterday, several thousand people who wanted to get a head start on the festivities and a jump on the crowds braved a midmorning downpour to take advantage of the open gate. The storm caused minor delays for exhibitors and some anxiety for fair organizers who remember the four days of rain last year that kept attendance to 250,000.

In the rabbit hutch, Christopher Tucker, 2, of Rockville wasted no time getting acquainted with the bunnies. Pulling away from his mother's arms, he gently grabbed a smoked-pearl Netherland Dwarf bunny by the head and planted a soft kiss on the rabbit's nose. One tent over, Kristen Hoelzer, 3, and her sister, Kimmy, 2, who had come to the fair with their parents from Herndon, squealed in delight as they watched a cow get a haircut.

For some young exhibitors, such as Cynthia Sorensen and Heather Polner, two 13-year-olds from a Gaithersburg apartment complex, being involved in the fair this year may have lasting impact on their lives. The teen-agers raised rabbits, pigs and a calf this summer in a class at Ridgeview Junior High School and entered their bunnies in the fair competition. Polner wants to be a farmer "if I get rich enough" and Sorensen wants to work with animals.

"I think it's silly that people are making the animals extinct," Sorensen said. "It's important that with all the high-tech stuff that we don't forget that animals got us started."