THREE MILES beyond the Beltway is a small ocean -- with waves, a beach, scores of sunbathers. A quirk in the geophysical system? No, it's Wild World, 80 acres of recreational irrigation amid the cornfields of Largo.

Wild World delivers what it promises: the most fun you'll have in a bathing suit within a half-hour's drive of the Capitol.

Eight fans hidden in a white bulkhead create an ocean's worth of up to four-foot waves for as many as 1,500 bathers in Wild World's million-gallon pool. Where the surf ends, there begins acres of plastic beach covered with up to 6,000 sunworshipers in chaises longues.

Wild World's latest addition is Paradise Island, a 500,000-gallon aquatic escape encircled by the 780-foot Lazy River. A man-made current sends rafts gently down the river while island bathers enjoy rides that include two "shotgun slides" that drop you into the island's cloverleaf-shaped pool.

Nearby, twin corkscrew-shaped slides are designed to spin riders down 25-foot water-fed tubes and into the pool. Also, there are two kiddie slides and (for those who always wanted to walk on water) lilypad paths.

Aquatics supervisor Joel Schlossberg says 24 of the park's 60 full-time Red Cross-trained lifeguards will have island duty. And in the center of Paradise Island, a 20-foot waterfall cascades over a bench full of about 30 islanders, while dozens of others lounge on chairs. (Bathing suits must be worn in all swimming areas.)

If you're looking for a joyride, head across the park where the Wild One sits, a huge white wooden monster waiting to shake the dickens out of those hoping to tame it. The 70-year-old roller coaster, brought here from Paragon Park in Nantasket, Massachusetts and reassembled, is rated sixth in the world by the American Coaster Enthusiasts. Only the stout-hearted (or is it the foolish?) keep their eyes open while the Wild One whips through 98-foot drops at 52 degrees.

After a harrowing, twisting 60-mph ride, your coaster car enters the final surprise -- a sharply banked hair-raising helix. Few riders notice the historic mansion (some say it's haunted) just a few yards away.

After a recent ride, a small girl -- shorter than the 48-inch height required to ride -- sat in the tall green grass pouting as her excited brothers returned from the Wild One.

"There, there now," comforted the mother, wrapping her arms around the little girl. "Maybe you'll be tall enough next year."

The under-48-inch set still has plenty to do, as do the non-daredevils or infrequent bathers. Wild World also has a choice of eight live shows ranging from Broadway-style musicals to a reptile revue to Cinema 180, a small sensurround-like movie theater.

The most delightful surprise at the park is the quality of the live shows, particularly the newly added country "Pickin' 'n' Kickin' " and "Broadway Magic" productions. Never have young adults worked so hard at a summer job.

And that's the way Melinda Grable, Wild World's new director of entertainment, wants it.

"Our audiences really want to be entertained," says Grable, who has chosen the most popular scenes from such hits as "42nd Street," "Yankee Doodle Dandy" and "West Side Story," to be performed along with short salutes to George M. Cohan and Duke Ellington. Grable spent a decade producing shows for Tennessee's popular Liberty Land park, where she directed Scott Taylor, now appearing in the Broadway production of "Cats" in New York, and then high-school gymnist Eric Henderson, seen in Michael Jackson's "Captain Eo" video. (Henderson, now a consultant to Wild World, choreographed the dance routines.) Grable has dipped deeply into the local talent pool and has come up with wonderful results.

"The range of personalities and experience, and nationalities, they're all so diverse," says Grable. "It really has worked out beautifully. We've got it all. Rather than try to make them all look alike and sound alike, I wanted them to look like themselves and be the very best they can be. I think the audience can identify with that."

Smaller than a lot of theme parks, Wild World caters to families, especially younger ones who'll like Kiddie City: a petting barn, puppet shows, hall of mirrors, a carousel and a baby roller coaster. The walkways are sloped gently, perfect for strollers (which are available at no charge), and wind through the neatly kept park. Landscaping features more than 7,000 annuals planted between magnolias, furs, maples and holly trees. Until the late '70s the park was a wild animal safari kingdom, which accounts for the widely planted patches of bamboo and a wealth of tall jungle grasses. WILD WORLD --

is open 10 to 10 daily. Admission is $11.95 for adults; $9.95, children 4 to 10 years; $7.95 seniors 60 and older. That covers all rides, shows and swimming areas. The admission for all guests is reduced to $7.95 after 5. Season pass: $34.95. Discount coupons, $3 for adults; $2 children, are available at Giant Food stores. Parking is $2. Group rates for 15 or more. Call 249-1500. There are four restaurants on the grounds; picnics cannot be brought into the park. From the Beltway, take Route 214 east for three miles; or Metrorail Blueline to Addison Road and a T-10 or T-11 bus.