Audrey Davenport says it will not rain on Maryland's Western Shore this weekend, when Calvert County holds its first annual "Mayfest," a y'all-come celebration that Davenport more or less invented.

"It wouldn't dare rain," she said. "Not after all these hundreds of people have worked so hard to get everything ready." What's ready includes everything from a seafood pigout and dance at the armory in Prince Frederick to the Southern Maryland Celtic Festival in Huntingtown.

Quick now: Where is Calvert County?

"We're just down the street from the White House," Davenport said. She's stretching it a bit, but if you stay on Pennsylvania Avenue long enough, which is to say 30 miles, there you are in Maryland's smallest county. Or take Route 4 south from the Beltway.

And hey, they'll be waiting for you, with maps and schedules and self-guided or bus tours, fairs, fishing tournaments, raft races and a sailboarding regatta, puppet shows, tours of gardens and historic homes (Calvert County harks back to 1654), flea markets, arts and crafts shows, nature walks, antique automobiles, and music and entertainment of all descriptions, including clog-dancing.

Did you know that there's a Lower Marlboro? Well there is, just off Route 4 (on 262), and it used to be a considerable port on the Patuxent River, welcoming ships from all over the world. The seaport silted in, but Olde Lower Marlborough Town is ready to welcome all comers Saturday, with home tours, old-time music, lunch served by the ladies of the community and demonstrations of quilting, stained-glass windowmaking, fishnet-weaving and chair- caning. Things will be a lot quieter Sunday, but they'd be happy to see you in church.

The countywide festival centers on Prince Frederick because, "Well, Prince Frederick tends to get overlooked; people cut off to Chesapeake Beach or head on down to Solomon's Island," said Lynn Frazer, honcha of the county tourism council. Saturday, along with the Feast of the Tidewater (all you can eat for $12.50, children $6.25) and the Mayfest Dance (free), both at the Armory, everybody in town who has something to show or sell will be out on the sidewalks smiling at you.

And don't overlook North Beach, which has long since cleaned up the act that got it ruled off-limits to servicemen during World War II. Saturday will feature a "Run for Fun" (call 301/257-2554) and dancing round the Maypole in the park, plus special activities for senior citizens (30l/257-2549). Sunday, there's a raft race (301/257-2554) and a fair along the waterfront.

Actually this weekend was supposed to be the Second Annual Calvert County Mayfest, which Davenport, Gloria Hall, Ada Gollub and Mildred Hairston dreamed up in February of '82, "but we discovered that it takes more than a couple of months to set up something like this," Davenport said.

The idea is to drum up business, of course, but it doesn't sound crass the way Davenport tells it. "We're facing about 30 percent unemployment among our young people, and we must create some opportunities for them. Tourism is the cleanest industry there is, and I think Calvert's about the nicest place there is, so we're trying to get people to look us over." Davenport has hired several once-aimless local youths as her Penwick House restaurant in Dunkirk has prospered, and hopes to see the same thing happen throughout the county.

Maps, programs, tickets and whatever will be available at visitor centers on Route 4 near the county line (north and south) "and wherever else we can think of to put them out" Davenport said.

If you want to pass for a native, talk moderately soft and slow, and pronounce it "Culvert Cahnty."