THE BLUE-SHIRTED man isn't a player, but at certain moments in a ballgame you would swear he's having more fun than anyone else on the field.

"Hrrrrrrrk!" he growls through his mask as he points a knee sideways, pumps both fists and holds a dramatic pose for two long seconds. Translation: Strike three!

Soon your attention shifts back to the pitcher, to the runner on third, to the batter coming up to the plate.And you don't really notice the masked man again until, crack, there's a grounder to short, a throw to the plate and . . . .

"Out!" yells the umpire, brandishing those fists again, leaping like a kung fu fighter, stamping the moment with his own exclamation point.

Wow. That does look like fun.

Indeed, local umpire John Porter says, the job is a gas. "Emotionally and physically, you put it on the line," he says. "I could equate it with assertiveness training or thrill-seeking. You're in a stadium, surrounded by hundreds of people, and every single decision that you make is gonna be hated by half the people. And for the individual who can handle the intimidation of those occasions, umpiring is a rush. I know a lot of people who umpire just for those occasions where people are gonna go crazy on the ballfield -- because {these umps} have confidence in their ability to handle those situations."

Yup, in case you were curious about becoming an umpire, a healthy ego is a must. Also, a knack for managing people. And a love of the game. Because unless you love baseball, you'll never stand the heat, the dust, the backaches and the occasional charley horse.

Certainly people don't get into umpiring for the money. In the adult-recreational and youth leagues where most of the work is found, the pay is skimpy -- as little as $10 a game. Men and women who toil on baseball diamonds almost always have a full-time job doing something else.

The same generalizations apply to local softball umpires and to soccer and rugby referees: low pay and a fair amount of fun.

And lots of opportunities. As all amateur league officials around here report, there's a continuing need for good umpires and referees, male or female (generally 17 or older). So, once you've completed your training and broken in as a rookie official, you can stay as busy as you want.

Here's how to get started. BASEBALL

Getting into action requires an outlay of $300 to $400, which buys a uniform (pants, shirt, jacket, cap, steel-toe shoes) and other essentials (mask, chest protector, shin guards, ball-strike indicator, plate brush). Recouping this investment may take 30 or 40 games, once you factor in transportation costs.

However, as veterans emphasize, umpiring is a diversion. "We umpire because we like baseball," says Milt Gustafson, an instructor with the Metropolitan Baseball Umpires Association. "Yesterday I was on a field where a young man from Blair High School pitched a no-hitter. It's really fun to see something like that."

The work provides exercise, but of an unpleasant kind: lots of crouching (for the home plate ump) and sudden, short sprints after minutes of standing still (for plate and base umps). THE TWO MAIN organizations in this area are the Northern Virginia Baseball Umpires Association (703/978-3601) and the Metropolitan Baseball Umpires Association (301/843-2752).

Porter, who's in charge of training for the Virginia group, says that all newcomers must take a 55-hour course ($35) spread over eight weeks between late February and April. The evening and weekend sessions are held in gymnasiums and on baseball diamonds. Graduates are assigned to youth league games (ages 10 to 13) and as they prove their abilities may be promoted to higher levels of competition: older youth, high school and adult recreational. To qualify for college-level ball, umpires must complete two more NVBUA spring courses.

The Metropolitan group's clinic ($20), starting in January and running eight weeks (one two-hour session per week), prepares umpires for high-school competition and below. SOFTBALL

On the diamond, softball umpires do what their baseball counterparts do: call balls, strikes, fair balls and foul balls, and render decisions on plays.

As with baseball, it's vital to get into position to see a play well. But doing that can be hard. Here's why: Most softball leagues can afford to use only one umpire, so that person must frequently dash from home plate to other parts of the infield.

Though softball may seem more casual than baseball, the potential for on-field tumult is equally high in both sports. An umpire who wants to stay in control has to project power that borders on arrogance. Says umpire Chick Montrose, "You have to be self-assured enough to say, I'm sorry, fellas, I am right. I do know this rule.' "

At times, an out-of-position umpire must summon the courage to bluff -- to say with conviction that he saw something he really didn't see. The rule of thumb, umpire Mark Ingrao says, is to go with a positive call. "So if someone says, Hey umpire, that guy left first too early,' and you were watching the runner at third, you give a big safe call and say Safe!' "

Won't that tick people off? Ingrao chuckles. "Well, let me say that in umpiring you're going to please 50 percent of the people 100 percent of the time."

Softball umpires' uniform and equipment outlays are in the $200 to $300 range and game pay is $15 to $25. Umps who work games outside the area get travel reimbursements, but typically not higher fees. TWO BIG OUTFITS in this area are the Greater Washington Softball Umpires Association (slow and fast pitch; 301/384-8496) and the Fairfax Softball Umpires Association (slow pitch only; 703/329-7000 or 703/922-0241).

Chick Montrose, an official with the first group, says the course for newcomers ($25) is held in weekly sessions from mid-February through March. In April, the grads work a charity tournament under the scrutiny of senior umps. Based on their proficiency, rookies are then assigned to either a youth or adult rec league.

The umpire-in-chief of the Fairfax group, Mark Ingrao, reports a similar training and assignment setup (the class costs $30). Ingrao says FSUA umps work games in Arlington, Fairfax, Herndon, Reston and Falls Church. OTHER SOFTBALL CONTACTS -- In Maryland: Metropolitan Umpires, 301/776-0138; Southern Suburban Umpires, 301/627-0608; Tri-State Umpires, 301/856-2029; White Oak Officials, 301/445-0054. In Virginia: Commonwealth Umpires, 703/352-1267; Greater Potomac Umpires, 703/590-3782; Northern Virginia Fast Pitch Umpires, 703/938-8672; Potomac Valley Officials, 703/430-1439. In Washington: D.C. Board of Officials for Women's Sports, 202/563-4483; Robinson Officials, 202/678-4612. SOCCER

Although people who train officials say they welcome pupils who've never played the game, it's a soccer truism that former players make superior referees. That doesn't mean you shouldn't jump in if you're a newbie. But be aware that you may have some catching up to do.

As a beginner, you will learn such things as how to get close to the play, but not so close that you hinder it; to run a basic diagonal while keeping linesmen and play in view; to blow your whistle with the proper intensity (trickier than it sounds); and to use the correct procedures when penalizing players. You will discover that learning the game's laws is not sufficient; you must also develop a feel for deftly interpreting their letter and spirit.

You'll also learn how vital aerobic conditioning is. "In a college game you run a good five miles," says Garrett Tucker, a Largo school teacher who has 18 months' experience as a referee. Five miles over 90 minutes -- no sweat, right? But when you work three games in a weekend, as Tucker often does, you must be able to pace yourself.

Typically, a new ref's first assignments will be in the lower reaches of youth competition, where the pay is $20 to $35 per game and the ref is obliged to teach the kids as well as police them. At the adult level, the money is better, but player and spectator emotions run higher, which can test a ref's ability to stay cool.

Necessities, including "boots" (cleats), uniforms (shorts, socks, shirts) and other stuff (whistles, flags, cards), run $150 to $250. THE THREE MAIN referee training groups are the D.C./Northern Virginia Soccer Referees Union (703/689-3442), the Capital Area Soccer Referee Association (800/442-2772 or 301/567-3347) and the Metropolitan Washington Soccer Referees Association (301/570-5889).

All offer clinics at least twice a year. These typically last 16 hours (spread over a month) and cost $30 or less. RUGBY

"A top-level referee is a hard-running cerebral athlete, capable of the most intense physical and mental exertion. . . . During the match, he is the sole judge of fact and of Law; he may not take advice; he may not alter his decisions; players may not dispute those decisions."

Reading Jeremy Turner's "The Complete Referee" makes a ref's work sound intriguing, even if you're clueless about the mechanics of rugby. As Turner tells it, the rugby ref is an exalted figure in an exciting game. Nigel Willis, a local official, shares that opinion. "There's little to no tolerance for talking back to the referee in a rugby game," he says. "Players who do it can be quickly ejected."

Playing experience is a plus, but teachers are used to working with neophytes. As with soccer, you must be fit enough to run a lot, know how to position yourself to see the ball and have a very solid grasp of the game's laws.

Don't look to rugby for a second income. Refs generally are not paid for their work. They do it for fun, glory and a love of the game. THE POTOMAC RUGBY UNION (202/543-6862) is the place to call for information about the referee instruction clinics, which are held year-round. "The Complete Referee," $34.95 (including postage), is available from USA Rugby, Colorado Springs. 719/637-1022. Next week in this space: Field Trips checks out the black bears of Garrett County. CAPTION: In her first game as an umpire, Carol Calder makes her pitch for respect during a softball game near Pentagon City.