I KNOW a one-word secret just aching to get out: lacrosse.

Called the fastest game on two feet, lacrosse offers the best of all possible worlds for the springtime sports spectator. On any given weekend afternoon you can throw on a pair of shorts and thongs, usually find plenty of stadium parking, lounge in cheap mid-field seats and catch world-class athletes in action -- fierce action. Lacrossers resemble gladiators: They go at it tooth and nail.

The game eclectically combines the best elements of other sports: the non-stop action of soccer, the finesse of basketball, the contact of football and the speed of ice hockey. But unlike those sports, lacrosse remains purely amateur. It's a unique experience.

"Just go see it," says Steve Stenersen, executive director of the National Lacrosse Foundation. "Once you do, you'll be sold on it."

As a fellow believer, let me share some tips on watching (and appreciating) North America's oldest sport. CATCHING THE GAME

Be sure to wear sunglasses. It helps you fit in with the crowd and has the added advantage of helping you follow the ball -- a hard rubber one about the size of a tennis ball that travels up to 90 mph over an area the size of a football field. It's easy to lose sight of it with all the running, passing, picking, scooping, jostling and shooting going on.

The object is to score by slinging the ball into an opponent's goal. Players carry the ball in a mesh pocket at the end of sticks varying in length from three to six feet. To shoot, a player whips his stick using a lever motion. In an average game you'll see 20 goals, many of which occur during a penalty situation in which one team loses a player, as in hockey.

The sticks also serve a defensive role; it's legal to hit an opponent's stick and body in order to jar the ball loose or to keep him away from the goal.

Each team fields ten players: attackmen, excellent ballhandlers and shooters who play offense near the opponent's goal; middies, who play both offense and defense, doing a lot of open field running; defensemen, usually the largest and most physical players who use the longest sticks; and a goalie, who must be crazy enough to stand in front of the goal and deflect 90 mph shots with a wide-mesh net and not much else.

Strategy and substitution have become quite sophisticated, so don't worry if you're overwhelmed at first. You'll pick up the rest the next game. THE WHO, WHEN AND WHERE

The top lacrosse teams play in either a club or collegiate league. But any way you slice it, the best lacrosse in the world is found within an hour's drive of Washington.

Playing out of Baltimore, the Maryland Lacrosse Club, comprised mostly of ex-All- Americans and considered by many the nation's supreme team, has won the last three national club titles. Seven of its team members played for the 1982 World Championship American team. Roughly nine other United States Club Lacrosse Association teams play in the Baltimore-Washington area, and the Lacrosse Foundation (Homewood, Baltimore 21218; phone 301/235-6882) can put you in touch with a game in your area.

At the collegiate level, four of the nation's top ten teams play nearby: Maryland, Navy, Virginia and Johns Hopkins, which won the NCAA title last year and is a perennial powerhouse. A tournament selection committee picks the best eight college teams to contend for the national championship; the location of the quarter and semifinals depends on the rankings (the finals are in Providence, R.I.). It's a safe bet some of the action will be taking place near Washington. LAX LINGO

Here's a short glossary of lacrosse terms that you may hear being bandied about on the sidelines. Some of them -- especially the penalty nicknames -- may give you an idea of what kind of action you can expect to see on the field.

CREASE: The circle, with a nine-foot radius, around the goal where only the goalie is allowed.

CHECK: Legal use of the body to ward off an opponent in possession of or attempting to scoop the ball.

CLEAR: The attempt to bring a ball down field.

CRADLING: Arm movement that uses the principle of centrifugal force to ensure the ball remains in the pocket.

CRANK SHOT: A low, hard shot on goal from the ankles.

FACEOFF: Begins each quarter with the ball placed in the center circle in the middle of the field between the sticks of two opposing players who attempt to get control of the ball when the referee sounds his whistle. A faceoff is also performed after each goal scored.

MAN-UP: The situation when a team has the advantage of an extra player because the opposing team has lost a man owing to a penalty, which usually lasts two minutes.

OFF SIDES: When a team leaves one half of the field with fewer than three players, not counting the goalie; a violation.

SIEVE: A term for a poor goalie; one who allows many goals.

SLASH: An uncontrolled, illegal use of the stick to hit another player; a frequent penalty.

QUICK STICK: The simultaneous catching of a pass and shooting on goal by a player. LACROSSE ACTION

The next few weekends offer key matchups in the Washington area that promise to be among the season's most exciting. Here's the schedule:

SATURDAY -- Maryland vs. Johns Hopkins, 2 p.m., Byrd Stadium, College Park. $4 adults; under 16, $2.

SATURDAY -- Virginia vs. Navy, 2 p.m., Scott Stadium, University of Virginia, Charlottesville. Take I-66 West to U.S. 29 South into Charlottesville; U.S. 29 becomes Emmett Avenue, which leads to stadium. Adults $3; under 12; $2.

SUNDAY -- Mt. Washington vs. Maryland Lacrosse Club, 2:30, St. Paul's High School, Baltimore. Take I-95 into Baltimore, taking Downtown Exit; turn right on Pratt Street and proceed one mile into Inner Harbor area; take Jones Falls Parkway (83 North) bearing left, turning into Falls Road; make left at third light to take you to the stadium. $2.

APRIL 27 -- Johns Hopkins vs. Navy, 2 p.m., Homewood Field, Baltimore. Take I-95 North into Baltimore, taking Downtown Exit; turn right on Pratt Street one mile into Inner Harbor area; take Jones Parkway (83 North), exit onto 28th Street turning right, make left on Howard to the stadium at 33rd and Charles streets. This is Hopkins' big homecoming day, so parking will be tight. $3.

APRIL 27 -- Virginia vs. North Carolina, 2 p.m., Scott Stadium, University of Virginia, Charlottesville. $3 adults; under 12, $2.

MAY 15 -- NCAA quarterfinals, location to be announced.

MAY 18 -- NCAA semifinals, TBA.

JUNE 7-9 -- Lacrosse International Weekend, Homewood Field, Johns Hopkins. For ticket information, call 301/235- 8512.