The Montgomery County Agricultural Fair, an annual event in Gaithersburg since 1948 and one of the largest county festivals in the eastern United States, opens for pre-fair activities this weekend and has its official kickoff Monday.

Milling through the arts and crafts booths and the livestock showings this year will be a special group of visitors: about half a dozen severely ill children from the Montgomery County area.

"We wanted to reach out and offer those kids something they hadn't had before," said Becky Brashear, assistant executive director of the fair. The fair board will honor these children at the official opening and invite each one back for his or her own VIP day at the fair, she said.

These activities follow a visit by fair officials and participants to Children's National Medical Center of Washington in late July, during which small live animals, games and educational displays from the fair were brought in so children who normally would not be able to attend the fair could experience some of the fun.

"{This} program has turned out to be one of the best things we have ever done in a cooperative effort," said fair board president Robert N. Stabler. "Officials . . . believe this is a community-service oriented project in which everyone benefits . . . especially the children."

Organizers hope to make the program an annual part of the fair and are raising money for the project by donating 75 cents from each photo button sold at the fair to a children's fund.

Over its nine-day run, the fair is expected to draw more than 350,000 people. Last year there were nearly 11,000 exhibits in the livestock, farm and garden, arts and crafts and home arts categories, and planners expect more this year.

Beef is the 1990 livestock species of honor, and cattle ranchers, nutritionists and professional chefs will be on hand to tout the industry. Visitors also will be able to step into a beef-dominated version of "Old MacDonald's Barn," where cow and calf pairs will be on display and area beef producers will discuss local and national breeds.

Stabler believes that an agricultural fair plays an important role in a county that is rapidly developing. But he acknowledged that the fair must market itself more aggressively. For the first time, a visitor satisfaction survey will be conducted during the week.

"The original purpose was to promote agriculture, and that is still the real emphasis," Stabler said. "But we are trying some new things. The entertainment end of it . . . has nothing to do with agriculture, but it draws the public in."

One sign of Montgomery County's changing demographics is the inclusion this year of a multicultural day, featuring booths with African, Afghan, American Indian, Hispanic, German and Polish themes.

The fair also serves as a showcase for the county's chapter of the 4-H Club, an organization that promotes educational programs for children and young adults. Hundreds of 4-H'ers will conduct exhibits, from livestock to wood furniture to baked goods.

Heather Hamm, 17, of Clarksburg, will be showing seven purebred black Angus in the beef cattle competition. Hoping to sell two of her entries to raise money for college, she said that the fair is "the best sale that I'm in. There are other shows, but this is the most important. It's the big finale to a lot of work."