A mix of the old and the new greeted the first visitors to the 50th Annual Prince William County Fair, which opened its gates at noon yesterday. From the familiar--baby beauty contests, country music and carnival rides--to the foreign--alpacas, dancing bears and the ominously named Inverter--organizers of the state's largest county fair hope to attract their biggest crowds ever.

"We have an entertainment package that will bring perennial fairgoers and people from outside the county," said Randy Fox, fair general manager, who estimates that 100,000 visitors will cram the 85-acre fairground on Route 234 just south of Manassas during the nine-day event.

The fair, which is sponsored by the Prince William Veterans Farm Club and has the theme of "It's an Udderly Good Time," was first designed to encourage youth to become farmers. Today, the crowd-pleasers are the truck and tractor pulls held tonight and tomorrow, and the demolition derbies next week. Agricultural attractions, such as prize goats and crowing roosters, are overshadowed by the 32 carnival rides, including the Ferris wheel and the Inverter, whose swinging arm flips 44 people upside down, provided by Deggeller Attractions.

"We get kids who don't know a goat from a sheep or the difference between a dairy and beef cow," Fox said, adding, just in case, that sheep have wool and beef cows are fatter than their dairy cousins. "We have only five or six dairy farms in Prince William County, but we want to keep agriculture a part of fair. So a lot of our animals come to us from Fauquier."

Or Peru. Barbara Bramlette brought two Peruvian-born alpacas, Santana and Desi Arnaz, from her alpaca farm in Gainesville. (She had to leave Lauren Bacall, Rita Hayworth and her 76 other alpacas named for movie stars at home.)

The four-foot tall alpaca, with its dark eyes and a tuft of hair on its forehead, looks like a llama covered in wool. Its fiber, which is softer and less itchy than sheep wool, is becoming increasingly popular in the United States.

Alpacas, Bramlette said, also make great pets.

"Alpacas are very gentle. They're cheap to maintain because they're not big eaters. They don't spit [except at each other]. They're easy to raise and love children," goes Bramlette's sales pitch. And they cost only $10,000 to $100,000 each.

Bramlette wasn't the only person selling things at the fair. Among food vendors peddling sausage and racks of ribs was a pizza stand run by the Bull Run Troubadours, the local chapter of the Society for the Preservation and Encouragement of Barbershop Quartet Singing in America.

Troubadour Joe Keady, 55, of Montclair, said the pizza booth is not only the all-male a cappella group's only fund-raising event, it is its most important recruiting venture. A number of the troupe's 30 members were lured into the fold with pepperoni pizza. In addition to tutoring in four-part harmonies and choral singing, Keady said members are required to take classes on making pizza.

Pizza and alpacas will be available from noon to 11 p.m., with rides and games opening at 2 p.m. Daily general admission for the fair is $10 for adults and $4 for children 3 to 6 and people 60 and older. Children 2 and younger get in free. Proceeds are reinvested into next year's fair, organizers said.

In honor of the fair's 50th anniversary, tickets bought at the gate Monday will be half-price, and there will be a fireworks display Tuesday.

Yesterday's events included competitions in home arts--from jam- and jelly-jarring to quilting--with nearly $30,000 in blue-ribbon prize money being given away, said Sandra Markhamm, home arts organizers and one of 300 volunteers employed by the fair. A bake sale of the breads, cookies and cakes competing for first prize raised several hundred dollars, which will be donated to local charities.

Yesterday's feature event were the 42 boys, ages 9 to 18 months, dressed in their Sunday best who stumbled down the runway in the baby beauty contest. Eighteen-month-old Kyle Cole was contestant No. 38, marked by a sticker on the back of his blue plaid button-down shirt. His mother, Angela Trammell, 18, of Manassas, bought Kyle new leather loafers just for the contest.

"If you have to carry your child, that's fine. If your child is snoring, that's okay, too," announcer R.C. Wolfenden of WFAX-FM in Falls Church instructed parents. "We just want the babies happy."

While Kyle waited his turn, he pursed his lips and yelled at the black-and-white dairy cows reclining behind the bleachers. Every now and then he would clap, distractedly, for the other competitors.

When Kyle's turn finally came, he directed his baby-blue eyes and chubby cheeks toward the judges and waved.

"We try to concentrate on the face, not the clothing or hairstyle or their expression," said judge Joan Flory, of Fauquier County (an outsider, to avoid favoritism).

"But of course it's wholly subjective," said Holly Bridges, of Herndon. "They're all cute, and every one of them cracks me up."

When Wolfenden announced the numbers of the contestants who would go to the next round, Kyle's was not called. But Kyle didn't seem to mind; he had wandered off to talk to the cows.

What's Happening at the County Fair

Today

10 a.m.

Northern Virginia District Dairy Show: showing and fitting

noon

Gates open

1 p.m.

Northern Virginia District Dairy Show: type classes

2 p.m.

Midway opens (weather permitting)

Children's Activity Barn opens

7 p.m.

American Tractor Pullers Association (grandstand)

Tomorrow

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

Monday

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

2, 4 and 8 p.m. today

4, 6 and 8 p.m. tomorrow

Katy Benko

6 p.m. today

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