"I'm going to stop her this time," vows Cornelius Mackall of Prince Frederick, onetime world champion oyster-shucker.

"Her" is Heidi Harrelson, a professional oyster-shucker from Apalachicola, Florida, the first woman and the first nonMarylander to win the natioal crown -- beating Mackall by 19.2 seconds. Harrelson recently took third place in the world championships at Galway, Ireland, and will defend her national title at the St. Mary's County Oyster Festival this Saturday and Sunday. The local shuckers are ready for her.

Gathered around a table at Evans' Crab House in Piney Point, five professional shuckers who have placed high in the contest in recent years are talking about the championships and about the dying profession of oyster-shucking.

The race, explains Bernice Newton of Mechanicsville, who placed third in the women's division last year, is not always to the swift.

"The neatness of the oysters counts, too. If you get pieces of shell in it, or if the oyster's not cut clean from the shell, they add seconds to your score," she says. Last year Harreson shucked 24 oysters in 2 minutes, 19 seconds.

In several ways, the contest differs from shucking oysters in a packing house or restaurant, according to the contestants. First of all, there may be 20,000 people watching.

"You don't know how bad you shake when you stand up there," says Newton.

"Usually you get up a rhythm, but if you've only got two dozen in front of you -- " shrugs Ronnie Evans, another former national champ. "If you lose you go out the back way, because somebody probably bet on you."

The oyster season in Maryland has just opened, and the packing houses, which generally operate from September to March, are just cranking up for the season.

"With the weather warm, oysters are hard to get into," says Ruth Smith, who works at a packing plant in CalvertCounty. "We use a nipper, or breaker. It's a wheel that spins around. You stick the oyster in it and it knocks the end off."

"But if you get a hard oyster in the contest and you're used to putting them in the machine, you're finished," says Newton.

The breaker, and, sometimes, conveyor belts that carry oysters to human shuckers, are about as automated as oyster-shucking has become in Maryland. State officials say that shucking machines are in use in Washington state and in Louisiana, but that demonstrations of the machines here have been unsuccessful so far. Packing houses have almost given up looking to machines to solve the problem of the perennial shortage of shuckers.

"It's a cold, wet and dirty job," says Newton, who works in her parents' packing house and restaurant business. "It has to be cold, because they hose it down all the time."

"I got into it 'cause I needed a job," says Mackall. "I wish I was in something else. I never liked it, never did."

But Mildred Myers, who works with Mackall in a Calvert County packing house, likes shucking "because you get paid for what you do."

"You're on your own," says Myers. "You work if you want to and stay off when you want to -- unless there's an order they want to get out. You don't get paid by the hour but by the amount of oysters you shuck."

A fast, experienced shucker can make $6 to $8 an hour, but if there are no oysters to shuck you may be given tomorrow off -- without pay. Work is seasonal, and when the season ends shuckers look for other work.

Mackall gets odd jobs. Smith, who has a second job cleaning a school at night after working mornings in the packing plant, also cuts tobacco when the harvest begins in late summer. The 13th annual St. Mary's County Oyster Festival will be held Saturday and Sunday, noon to 6, at the fairgrounds on Route 5 south of Leonardtown. In addition to the contest, (finals Sunday afternoon), there will be shucking lessons from the experts, an amateur shucking contest, square dancing, craft exhibits and oysters -- raw, fried, stewed, scalded and in chowder. Other food will also be on sale. Admission and parking: $1.

If you can't get away this weekend, oysters will also be featured at Chesapeake Appreciation Days, October 27 and 28 at Sanday Point State Park in Annapolis, and at Tilghman Island Day, November 3 on Tilghman Island on the Eastern Shore.