Most of Fairfax County's cow pastures and hayfields have long since become sprawling subdivisions and self-service gas stations, but that didn't stop thousands from sampling the suburban version of country fun at yesterday's opening of the fourth annual Fairfax Fair.

The fair, featuring everything from a chili cook-off and hayrides to a parking lot display of heavy earth-moving equipment used by developers, got under way at noon on the tree-shaded grounds of George Mason University in Fairfax City.

Although the event didn't have the sawdust and grit atmosphere or peach preserve contests of an old-fashioned county fair, and although it smelled of a back-yard barbecue rather than of live sheep and goats, it was an excuse for residents of Virginia's most populous and affluent county to celebrate.

The Emerald Society Bagpipers were there. So was Fairfax County's police helicopter. There were clowns, a merry-go-round and even part of a 400-bed inflatable surgical operating room display from Fort Belvoir.

People ate Tutti-frutti Hawaiian Shaved Ice, bought sun visors inscribed with the name of the rock group Motley Crue, licked lavender-colored cotton candy and shook hands with politicians.

The Fairfax Fair was one of several outdoor celebrations in Northern Virginia yesterday.

In Alexandria, thousands picnicked along the Potomac at the Alexandria Red Cross Waterfront Festival.

The three-day event featured 15 tall ships from around the world. By the close of the festival at 7 p.m. today, it is expected to have drawn more than the 100,000 who attended last year.

"It was time to get out of the house," said Norma Dyas of Alexandria, as she bought ice cream cones for her two children at the Alexandria festival.

By 4 p.m. yesterday, about 40,000 people already had visited the fair in Fairfax, and Director Mary Markham was predicting a two-day turnout of more than 100,000.

Lorrie Mosblack, 26, of Annandale was one of hundreds who milled through the arts and crafts area. She bought a ceramic kitchen spoon holder shaped like a pig. "I have a pig-lover friend," she said. "She and I exchange pig things all the time."

Joan Demos, 57, who sold the spoon rest, said pig replicas are popular collectors' items now. "People also like owls, foxes and frogs," she added. "We have a silly frog night light over there that we made for a 42-year-old man, and he was just tickled with it."

Also wandering the university lawns that served as the fairground were some 250 volunteer aides, including Jean Lovell, 43. She moved from Fairfax to Virginia Beach last year, but she missed the fair so much she came back to help.

A highlight was the annual crowning of two civic-minded citizens as Lord and Lady Fairfax. This year's honorees were retired Brig. Gen. Archibald W. Lyon, who has been active in the Mount Vernon Citizens Association, and Lydia C. Heinzman, president of the Holly Hill Garden Club in McLean. The fair, sponsored by the nonprofit Faxfair Corp., reopens today from noon until 5 p.m. Admission is free, with parking on campus. Shuttle buses are available.