Chuck Farcus of Punxsutawney, Pa., a big man in a gleaming hard hat and aviator sunglasses, stood in the shadow of a massive oil-drilling rig, watching his crew of "roughnecks" sink a 50-foot hole in the Washington Monument grounds.

He said he figured his chances of hitting black gold were "doubtfull," though there had been a small gusher or muddy water. He'd just drilled the hole for the hell of it, he said, and for the sake of teh Smithsonian's 12th annual Folklife Festival, which begins today.

After a guitar-strumming Sen. James Abourezk (D-S.D.) helps kick off the opening ceremonies at 11 a.m., the festival will run daily through Monday from 10 a.m. to 5 p.m.

Under the broad theme of "communities" the Smithsonian staff has brought together cultures ranging from the oil-drilling "roughnecks" to the watermen of the Chesapeake Bay, from the Spanish-Indian culture of San Juan Pueblo in New Mexico to teachers from one-room school-teachers from one-room school-houses in the preintegration south.

To prepare for the extravaganza yesterday, carpenters worked frenetically near the 130-foot drilling rig at 14th Street and Constitution Avenue, readying a simulated coal mine for novice diggers to crawl through.

At the same site there will be gospel and blues singers, music and dancing from Mexico, silversmiths and saddlemakers, stonecarvers from the Washington Cathedral, a mininture oil refinery. Children can learn to make dolls from nuts and corn shucks, play games from Puerto Rico, or listen to tales of Br'er Rabbit and his friends.

At the museum of History and Technology nearby organ builders will tell how they give voices to metal pipes, sleeping car porters, sharecroppers and recent immigrants will talk about their lives, while wheelwrights their skills and, in the afternoons, visitors learn how to collect their own family lore.

On the steps of the Museum of Natural History, the Chesapeake Bay log canoe Rover, built in 1836, sits ready to sail again, its rakish masts now drawing attention to the traditions of the Chesapeake Bay.

On the same steps Sunday morning there will be a workshop to teach oyster shucking, and at 2 p.m. an oyster shucking contest featuring the 1977 champions from the Leonardtown, Md., festival competition.

There will be daily workshops, as well, on the art of making crab nets, the carrying of decoys, water skills and crafts, while nearby the native Americans of the Southwest demonstrate their crafts and cooking, the decor dance, the buffalo dance and the [WORD ILLEGIBLE] dance.

At the Renwick Gallery, meanwhile, Mexican artisans will fashion pottery and guitars, and demonstrate the making of masks.

Many Washington may be surprised to see familiar faces performing at the festival alongside the exotic communities from across the country.Near the Mexican area on the mounment grounds D.C. cabdrivers, street hawkers, fish market vendors and stree musicians will be swapping stores as arabbers - the street criers of Baltimore - peddle fruits and vegetables through the crowd from horse-drawn carts.

The list of films to be shown in the two museums ranges from the brutally dramatic coal-mining documentary "Harlan County, USA" (1:30 today) to "Pizza Pizza Daddy.O" (10 a.m. Monday) and "Home Movie): An American Folk Art" (4:30 p.m. Thursday).