To the dismay of the local fans, the Redskins lost to the Cardinals and Ola Mae Carter of St. Mary's County lost to Dave (Diz) Schimke, of Bow, Washington State, in the 18th annual oyster shucking contest held here today.

Schimke, a bearded 24-year-old lefthander who entered as the West Coast champ, bested Carter, 39, by shucking two dozen oysters in 2 minutes and 41.31 seconds, compared with 3 minutes and 38.01 seconds for the runner-up. The times included penalties for oysters that were cut or dirty when shucked.

Schimke's victory won him a $500 cash prize and the right to represent the United States in the oyster opening internationals next September in Galway, Ireland.

The suspense mounted during a long afternoon that included a demonstration by reigning world champ Jose Burke, of Galway, three amateur contests and men's and women's semifinal competitions.

There was little talk here of the scarcity of oysters or of the battle to save the Chesapeake Bay, their endangered growing grounds. Officials of the St. Mary's County oyster festival said there were a quarter of a million of the bivalves here for the shucking and the eating, and the only battle was over who could bifurcate bivalves most quickly and cleanly.

"We feel that this contest is just as important and exciting as the Mondale-Reagan debate and as the St. Louis-Redskins game," asserted the master of ceremonies, former Maryland House of Delegates speaker John Hanson Briscoe, who kept up a steady patter as master of ceremonies throughout the event.

"Each one of these oysters is cold and would rather stay closed, I assure you," he told several hundred onlookers watching the shucking contest.

Officials and contestants wore buttons saying, "Aw, Shucks" and "A Whole Lot of Shuckin' Goin' On," as thousands of oyster lovers streamed through the fairgrounds in the unusually bright, warm late October sunshine.

It was the second straight year that an out-of-stater walked away with the top prize. Today, last year's national champ, Sarah Hammond, of Urbanna, Va., came in third in the women's semifinals, after placing third last month in the 1984 world contest. (The only American to win the world title was Calvert County's Cornelius Mackall in 1975.)

Schimke, today's winner, said he's hardly ever been away from the state of Washington, except for a honeymoon in a California redwood forest. Earlier in the day, he and his male competitors from Maryland compared oyster shucking in their locales. He said he thought Maryland oysters were harder to open. In his corner of the country, he said, it was "boom -- in the bucket."

He said he was not especially looking forward to visiting Ireland, just to having a good time here today.

"You're the best I've ever seen, said Francis Cullison, 35, a St. Mary's County waterman who came in second to Schimke in the men's semifinals.

It was Schimke's third competition. Among today's participants, perhaps the most seasoned competitor was Heidi Ho Oquendo, 49, of Cocoa, Fla. A Florida shucking champ for 14 years and one-time national winner, she also holds the world's oyster-eating records of 43 dozen in 15 minutes and seven dozen in one minute.

She is no longer a professional shucker, however. Instead, she flips omelets for a living. Next year, she said, she plans to arrive a few days early to get in some professional shucking practice before the contest.

Almost as serious as the high stakes national competition were the amateur events that preceded it.

In the women's division, Linda Darrell, 25, of Baltimore, water quality technician for the U.S. Geological Survey, won for the second year straight. "I don't know what I'm doing," she said before the contest.

She was coached during the event by Tara Ricketts, of Lexington Park: "That's good. Go for it, go for it. . . . Don't worry what they look like, just open the damned things. You got it."

Darrell, who has a year-old scar on her left hand from her previous contest wore a glove this year for protection. But she managed to slice her right forefinger before compiling a winning score of a dozen oysters shucked in one minute, 36 seconds.