We may not be able to boast of coral reefs or tropical fish, but just outside the District Line and more submerged ships from the Civil War and both world wars than anywhere else in the world. In fact, the waters off Maryland and Virginia have been called the best areas in the world for wreck diving.

And besides the Atlantic graveyard, Washington is close to many unique, crystal-clear fresh water diving sites. Where else could a diver watch monster catfish dart behind a 65-foot steam crane in deep water? Although snorklers may be able to peer at the underwater exhibits, it is the scuba diver who touches and can truly enjoy what Washington has to offer underwater.

At present, there is only one dive shop in the District. But Tom Cooper, manager of the National Diving Center 1 (4932 Wisconsin Ave. NW), says he plans to open another in Washington. There are 14 others in Maryland and Virginia, including The Dive Shop (7502 Leesburg Pike, Falls Church), which is owned and operated by Bill McGehee, regional director of the major scuba organization on the East Coast. All have qualified instructors and all offer beginner courses in scuba diving. Course fees range from $65 to $120 for instruction, though some charge an additional $25 fee for open-water dives - required for basic scuba diving certification.

The National Diving Center's Dive Shop charges $95 during the summer months for complete instruction including the rental of wet suit, air tank assembly, regulator, pressure gauge and buoyancy compensator. The classes form monthly on Saturday mornings and most weekdays evenings. Bill McGehee, owner of The Dive Shop, says that scuba diving can be a safe and enjoyable sport for people of all ages as long as they recognize and yield to their particular limitations.If you have a respiratory or heart condition, scuba diving may not be for you. But for those in good health, diving is safe when coupled with proper instruction, good equipment and common sense.

McGehee stresses that only certified scuba divers should use scuba gear because only certified divers know the significance of the physics and physiology involved in breathing compressed air underwater.

He says novice scuba divers should not dive deeper than 30 feet unless they are thoroughly familiar with the U.S. Navy decompression tables and related charts, or are accompanied by an experienced, certified scuba diver or diving instructor.

Renting good equipment (Scubapro, U.S. Divers, White Stag) generally costs from $35 to $45 per day for certified divers. Gloves, booties, watch and depth gauge are recommended for both fresh- and salt-water diving but are not generally rented out.

The waters off the coast of Maryland, Virginia, North Carolina and Delaware are the resting places of thousands of wrecks from both government and privately owned boats. Small hand-carried souvenirs may be taken from the sunken vessels unless rules to the contrary are posted.

All dive shops periodically run chartered excursions to these dive sites because most wrecks are accessible only by boat. They generally charge $35 for Virginia and Maryland trips and begin at $60 for North Carolina excursion (usually two nights on a 45-foot cruiser).

Some Washingtonians take up scuba diving for the relaxation found in tranquil waters, but there are other attractions. Fishermen can add to the thrill of the sport through spear fishing; the only necessary equipment besides scuba gear is a spear or spear gun. Most dive shops offer seminars in this sport, after which a diver can catch whopping salt-water fish long after his friends have stored away their rods and reels. You would be able to fish year round in the neighboring ocean waters.

Many scuba divers and snorklers can also enjoy "oystering" in the Chesapeake Bay, though it's seasonal and there are limits on how many oysters may be retrieved.

Washington also offers some of the most exciting fresh-water diving sites on the east coast. These dive spots are rock quarries where underground springs have been inadvertently hit, submerging the site. Most are teeming with fresh-water fish and for the adventurous there is a wealth of underwater exhibits - from sports car to steam cranes.

But the waters are always cold, from 40 degrees to 50 degrees F, and since most body heat is lost through the head, hooded wet suits are required when diving in spring-fed quarries. In addition, underwater flashlights are necessary at 70-foot depths and always when diving at night.

Common sense is the adage for all divers, including snorklers. Most dive shops offer classes on proper skin-diving techniques and safe snorkling.

All quarries are privately owned and charge between two and three dollars per head. The National Diving Center 1 keeps a card catalogue of more than a hundred city sports divers, their addresses, phone numbers and times at which they are available for dives. The card system enables a diver to find a "buddy" and a ride to any area site. GETTING DEEP IN THE BRINY

Here are eight of the best salt-water diving spots in the area: CALVERT CLIFFS

A diver can find fossils of shark's teeth and vertebrae in five to six feet of water in southern Maryland. Divers should enter from a small beach, making the site excellent for snorklers, too. VIRGINIA BEACH

The famous triangle wrecks of three World War II freighters submerged in 80 feet of water are visible even from the surface. A boat entry is necessary, but snorklers and boaters may also peer at these silent remnant on bright, clear days. OREGAN INLET

In these North Carolina waters you will find a World War II German U-85 submarine 110 feet down. Again, a boat entry is suggested. POINT LOOKOUT

-Civil War souvenirs are scattered along the bottom in 12 feet of water where the Potamac meets Chesapeake Bay. There are also submerged Civil War boats in 65 to 90 feet of water. An easy shore entry makes this site good for snorklers as well as scuba divers. MOOREHEAD, N.C.

Two sunken German U-boats can be found side by side in 110 feet of water. A boat entry is advisable. OCEAN CITY

World War II vessels and various wooden ships can be found, along with some private craft, submerged in 65 to 110 feet of water. You can reach this site easily by boat, but you don't have to be a diver to see these wrecks - on sunny days they're visible from the surface. ON THE TRIAL OF THE QUARRIES

Here are three interesting fresh-water diving spots: STRASBURG QUARRY

Strasburg, Va. Extends to a depth of 45 feet, is inhabited by many fresh-water fish, including large catfish and bluegill. The wilderness facility would make an enjoyable day for the entire family. Call 703/869-1797 for seasonal schedules. WILLOW SPRINGS

Meyerstown, Pa. The diver will find good visibiligy in this 45-foot-deep quarry. Besides bluegill and gigantic catfish, the site sports a submerged steam crane, a 70-foot trawler and sunken sports cars. Relatively clear water makes this excellent for underwater photography. FORT McCORD

Edenville, Pa. Good visibility attracts divers from the entire area to the shallow, clear waters of Fort McCord. The visibility, ranging from 20 to 30 feet on sunny days, makes this quarry a haven for novice scuba divers and snorklers who may not feel as comfortable in some of the deeper, more challenging dive spots in the area. The 20-foot depths, coupled with an easy access to the quarry waters, make a day of enjoyable, effortless diving.