You bet it's hot. The streets are going soft, the white lines are beginning to curve and only the delirious are smiling.

But Washington veterans know cooler heads can prevail. Why not start with a ride on the subway, where the trains average 75 degrees, and the breeze from the tunnels is five to 10 degrees cooler?

While we're on things underground, try the catacombs of the Franciscan Monastery in Northeast, just five blocks east of the Brookland Metro stop at 1400 Quincy Street. The catacombs, built to resemble those of Rome, are naturally cool and can be toured daily, beginning at 9 and repeating on the hour.

Approximately 10 of the monastery's 40 acres are open to the public. The well-tended lawns and gardens are filled with roses, holly, azaleas and scores of such summer flowers as scarlet hibiscus, marigolds, begonias and zinnias -- a fragrant and lovely place to beat the heat.

Over at the Library of Congress you'll find "one of the coolest places in town," according to one exhibit coordinator. The temperature's set at 68 degrees to preserve some 350 paintings, sculptures, photographs and artifacts of the American Cowboy exhibit, which runs till October 2 at the Madison Building at First and Independence Avenue SE. Also in the library's collection is a complete selection of Jack London's tales about life in the Yukon. Bring a sweater.

Culture is cool at the National Gallery of Art. In the West Building at Sixth and Constitution Avenue NW, you'll find Gilbert Stuart's "The Skater," a seven-foot tall portrait of William Grant in colonial attire easing over the ice, and Robert Henri's 1902 depiction of "Snow in New York." If wet is where it's at, try "The Much Resounding Sea," painted by Thomas Moran in 1884.

The National Aquarium, the nation's oldest public aquarium, is kept at 70 degrees for the lucky thousand or so specimens of 175 species of native and exotic fish, turtles and sharks. The sharks are fed on Monday, Wednesday and Saturday at 2. You'll find this oasis in the basement of the Commerce Department at 14th and Pennsylvania Avenue NW. Adult admission is $1, kids' 50 cents.

From there, how about a trip to your local store for longing looks at the seafood on beds of ice. Be sure to spend a long time in the frozen foods section, too.

And of course you can always think snow. Ski Liberty (717/642-8282), the winter ski resort in Fairfield, Pennsylvania, offers grass skiing on Saturdays and Sundays. They'll outfit you with a pair of two-foot ski boots, with bull-dozer-like treads underneath. This kind of fun sells for $10 for three hours. An Alpine Slide and a swimming pool cost extra.

A mixture of shorts, sunglasses and ice skating is one sure recipe for beating summer heat. There's year-round skating at Mount Vernon Sports Complex (768-3222), Fairfax Ice Arena (323-1132) and Fort Dupont (581-0199). Lake Forest Mall ice rink (840-1215) will be open until August 21, when it'll close for good and be turned into movie theaters.

Speaking of which, why are movies always so cold in the summer and so hot in the winter? A couple of chillers to consider are "Psycho II," "Jaws 3-D" and "Twilight Zone." If they don't cool you off, try an icy scene from "Doctor Zhivago," rented from a video store and played on a video recorder.

One thing easy to find in Washington is homemade ice cream. "Sales are terrific. We're very pleased," says Mary Barber, sales manager for the University of Maryland Dairy, where the entire production process from cow to customer is on campus.

Swenson's Ice Cream Parlor, Jeffrey's and Bob's Famous Homemade Ice Cream shops all make the cold stuff at each of their locations. At Steve's, you can watch them make any of 55 varieties at either the 1514 Connecticut Avenue or 1258 Wisconsin Avenue shops.

For as little as $4,000 to $5,000, the Good Humor Company in Hyattsville will put you in the driver's seat of a truck pushing Popsicles. But selling ice cream is no way to get rich quick, so simmer down, advises truck sales manager Dick Gammon. He says drivers work as many as 12 hours a day, seven days a week for a top weekly take of no more than $350. Talk about meltdown of the American dreamsicle!

Taking a cool dip has got to bring down your temperature. If the beach drive is just too out of the way, consider the new wave pool at Cameron Run Regional Park in Virginia. If you're a city dipper, try one of the 19 public pools in town. Or stay home and take turns squirting a friend with the garden hose.

Skinny dipping has always gotten a lot of exposure in this town. However, we're not able to tell you where to go, you'll just have to uncover the spots on your own.

Hot weather cries out for daiquiris. The basic ingredients are rum, sugar and lime juice mixed with finely crushed ice. More often than not, strawberries or bananas are added to enhance the flavor. Served in a large goblet- style glass, there's no wonder why daiquiris are all the rage. They even look cool and refreshing. Some places in town best known for their renderings of the drink are: Mr. Smith's in Georgetown, Nickie's in upper Georgetown, Man in the Green Hat and Bullfeathers on the Hill, Rumors H Street and Flaps downtown, Cafe Rondo's Daiquiri Factory near Dupont Circle, Portner's in Old Town and the Bombay Bicycle Club on Duke Street. Casa Maria on the waterfront has a reputation for fishbowl-size margaritas and memorable sunsets.

At four dollars a crack, it's may be more fun to have these easy-to-make drinks at home and water the thirsty garden at the same time.

Harboring secret desires to feel the sea breeze in your face and be the captain of your destiny? Backyard Boats in Alexandria can put you out to sea in a Sea Snark for $250 or a Sunfish for $1,195. If it's a case of Big Daddy Warbucks, there's always the Catalina 38, which sleeps six for a mere $65,000. If you need sailing lessons, try the Annapolis Sailing School.

What if your economic boom hasn't started and buying a yacht is out of the question? Consider renting your dreamboat. The Tidal Basin Boat House at 15th and Maine Avenue SW rents paddle-boats. For canoes and rowboats, try Thompson Boat Center, Jack's Boats or Fletcher's Boathouse, all on the Potomac.

Is see and stuff more to your taste? No problem. The Washington Boat Lines has boats for waterfront shuttle cruises, cocktails, floating buffets, moonlight dance cruises as well as scenic and party trips. Call 554-8000. In Annapolis, try the Luncheon Cruise. The boat leaves the city dock at 12:30 every Friday and Saturday afternoon through September. For $6.60, you can have a lunch of fried chicken, cold buffet and dessert (cash0bar) coupled with a 90-minute cruise to the Bay Bridge and back. Call 301/263-0200, ext. 455.

Looking for a weekend of 50- and 60-degree temperatures, waterfalls and fjords? Try Iceland. Icelandair has four-day/two-night "Cool Off Weekend" packages starting at $474 through August 25. Call the Washington Travel Center at 628-9191 for information. Looking in another direction? Think about Alaska. This month, local radio station WASH (97.1 FM) is giving away a four-day "Beat the Heat" trip up the Northwest coast aboard "The Love Boat."

But long, expensive trips aren't neccessary. Only 13/4 hours away by car are the Luray (703/743-6551) and Shenandoah caverns (703/477-3115). The temperature is a constant 56 degrees, and tours last about 70 minutes.

Countless whitewater rafting businesses have sprung up along the banks of the Cheat, Youghiogheny, Gauley, Shenandoah and upper Potomac rivers. Some firms to call are Appalachian Wildwaters (800/624-0806), Outdoor University (703/548-3838), Potomac River Tours (301/530- 8733), Blue Ridge Outfitters (304/725-3444) and West Virginia Whitewater (304/574-0871).

But the heat doesn't have everybody down. Harry Miller, shop foreman at ARA of Maryland, a Landover outfit that installs auto air-conditioning units, seems to be enjoying it.

"We're busier than hell!" says the Delaware transplant. Sales are "increasing every week. In the Washington area, when you say $650 or $675, people jump on it. I've never seen anything like it!"