Half a century ago, a group of World War II veterans trained as farmers under the G.I. Bill decided to organize a Prince William Veterans Farm Club. Immediately, they began looking for something for their club to do.

"If the club was going to amount to anything, we needed to have a function," recalls Joe Johnson, 75. "So we had a fair."

The first Prince William County Fair ran three days and had four barns filled with cattle exhibits. It was designed to encourage youngsters in the county to go into farming.

The fair promptly lost $1,200.

"That's why we kept going, to pay off the debt," said Johnson, laughing. "So we all planted corn on the fairground to pay it off."

Johnson and the 40 other original members of the club harvested just enough corn to hold the fair the next year. And that year they made money, and since then, the Prince William County Fair has grown into the state's largest county fair.

On Friday, the fair opened its gates for the 50th year. In honor of the fair's 50th anniversary, tickets tomorrow will be half-price, and there will be a fireworks display Tuesday. Organizers hope the fair's nine days of country music shows, tractor pulls and dancing bears can attract some 100,000 people.

Over the years, the fair, on 85-acres on Route 234 just south of Manassas, has changed dramatically. Today, a Ferris wheel and carnival games take up as much space as the barns, and the real crowd pleaser is the annual demolition derby, which will be held Wednesday and Thursday at 7:30 p.m.

"We still have a pretty decent cattle exhibit, though its nothing like we used to," said Johnson. "And most of the cattle comes from out of the county."

All but six members of the original veterans club have died or dropped out. Those who stayed--Johnson, Kemp Clemen, Robert Tyrrell, Sidney Flickinger, Robert Beahm and William Young--are the county's elder statesmen, responsible for creating one of Prince William's cultural touchstones.

Like the fair he started, Johnson has grown up with Prince William County. After serving on a cargo ship in the Navy during World War II--"I was one of the lucky people. No one shot at me, and we didn't shoot at anybody," he says--Johnson returned home to a dairy farm. Over the years, Johnson "moved from the county into the town into the city, without ever moving from the same house."

And during that time, he watched generations of children grow up with the fair.

"I've watched kids go through those barns for 50 years, and I'm kinda proud of what I've seen," Johnson said. "There's something about letting those kids take care of livestock. It shows a kind of responsibility you can't teach anywhere else."

What's Happening at the County Fair

Today

noon

* Gates open

* Midway opens (weather permitting)

* Children's Activity Barn opens

* 2 p.m.: Children's Pet Show: cats, rabbits, hamsters, others

* 4 p.m.: American Tractor Pullers Association (grandstand)

5 p.m.: White Star Marching Corps of Northern Virginia

Tomorrow

9 a.m.: Judging of rabbits

noon: Gates open

2 p.m.: Midway opens (weather permitting)

Children's Activity Barn opens

Baby contest, boys 19-36 months

8 p.m.: Ultimate Championship Wrestling (grandstand)

Tuesday

9 a.m.: Judging of poultry

noon: Gates open

1 p.m.: Judging of dairy cattle: showing and fitting, followed by type classes

2 p.m.: Midway opens (weather permitting)

Children's Activity Barn opens

8 p.m.: The Fox Brothers (grandstand)

9:30 p.m.: Fireworks

Wednesday

9 a.m.: Judging of dairy goats

noon: Gates open

1 p.m.: Judging of sheep

2 p.m.: Midway opens (weather permitting)

Children's Activity Barn opens

2:30 p.m.: Judging of second home arts exhibits (building closed during judging)

7:30 p.m.: Demolition derby (grandstand)

Thursday

noon: Gates open

2 p.m.: Baby contest, girls 19-36 months

Midway opens (weather permitting)

Children's Activity Barn opens

7 p.m.: Judging of swine

7-10 p.m.: WPWC gospel show

7:30 p.m.: Demolition derby (grandstand)

Friday

10 a.m.: Judging of beef cattle

noon: Gates open

1 p.m.: Judging of ponies

2 p.m.: Midway opens (weather permitting)

Children's Activity Barn opens

7 p.m.: Crescent Moon

7:30 p.m.: Presentation of special awards and recognition night

8 p.m.: The Wilkinsons (grandstand)

Saturday

noon: Gates open

2 p.m.: Midway opens (weather permitting)

Children's Activity Barn opens

Children's Pet Show: dogs

6:30 p.m.: Rodeo (grandstand)

Ongoing Featured Entertainment

Matt & Robyn

5, 7 and 9 p.m. daily

Ken Holloway

4, 6 and 8 p.m. tomorrow

Sh-Boom

6 and 8 p.m. Wednesday and Thursday

Comedy Safari

4:30, 6:30 and 8:30 p.m. daily

Bear show

4, 6 and 8 p.m. daily