FEAR NOT. Those eerie, luminescent shapes spiraling through the night sky this weekend are not the advance guard of some alien invasion.

They are boomerangs. And they are your friends.

For more than a century now, the boomerang has suffered a bum rap, the victim of British ignorance, not Aboriginal brutality. The British, who began colonizing Australia in the 1800s, carelessly referred to anything thrown by the natives as a "bumerang," thereby lumping the small boomerang used for sport into the same category with the larger, lethal killer-stick.

The two are not the same.

"The notion exists that the boomerang is a killer device," says Benjamin Ruhe of Washington, who helped found the U.S. Boomerang Association in 1979. "But that's wrong . . . The boomerang is no more dangerous than a ball or a bat. With any sense of care, you're okay."

Ruhe, who is considered one of the foremost boomerangers in the world, is the organizer of the second annual "Night Korobari" boomerang throw Saturday night on the polo field in West Potomac Park. In a twist on standard boomerang competitions, the Korobari will use devices studded with capsules of cyalume, a glow-in-the-dark substance that produces a spooky but poetic trajectory.

Although competition models can weigh as much as two pounds, most boomerangs barely weigh several ounces. Cut usually from plywood and coated with lacquer or polypropylene, the modern boomerang is too light to do any real harm. It is simply designed to fly.

But don't ask how. It would be hard to imagine a more contradictory object than the boomerang, a device that has prompted countless research projects and doctoral theses. Built around myriad complex aerodynamic laws and physical properties, ranging from the principle of gyroscopic precession to Newton's Law of Motion, the boomerang is nevertheless quite simple to master. After just 30 minutes of practice, an absolute novice can have the boomerang (or " 'rang," as it's called in the business) returning reasonably close to its point of origin, given a decent arm and close attention to the wind.

It is best to pick a large, flat area such as a public park or an empty field in which to throw a boomerang. A calm day is essential, as boomerangs cannot be controlled in winds in excess of 12 miles per hour. The boomerang is held loosely by either wing and thrown at a 45-degree angle to the wind with a motion similar to that of a baseball pitcher.

The release point controls the height of the trajectory (high release, high flight, and so on), but it is immediately clear that the boomerang's flight action is unlike anything else. It appears to flop over, hover, bank sharply and careen out of control before quietly landing.

Its idiosyncrasies are matched by the people who give it flight. Informal polls conducted by the USBA found that most 'rangers tend to be highly intelligent, free-thinking souls, many of whom work in the scientific field and enjoy tweaking the nose of social or physical laws.

"The sport has a large eccentric population," says Ron Tamblyn, a former philosophy honors student at the University of Maryland who, along with partner Mike Forrester, now manufactures boomerangs at their Flying Trees Ltd. company in Wheaton. "People who know 'rangs are there for keeps. It's a special little skill, kind of mysterious. Most people aren't hip to it."

For instance, boomerangers regularly trek to the international dateline in Waiyev, Fiji, just so they can throw their 'rang into yesterday. On December 31, the same would-be rebels toss their devices into next year.

In Europe, 'rangers have thrown into Soviet territory and back or over the Berlin Wall, while Americans take pride in standing in the Southwest and clearing four state lines (Utah, Colorado, Arizona and New Mexico) at the point where the states meet.

But Frank Donnellan of Australia and Barnaby Ruhe (Benjamin's nephew) have taken the sport beyond devilish to dangerous. Donnellan is best known for throwing his boomerang out one window of a moving car and then catching it through the other, while Ruhe became the first to successfully execute the William Tell trick, slicing an apple in half off his own head with a throw.

Although the boomerang will always be a vital part of Australian history, it is the Americans who have come to dominate the sport in recent years. While the USBA counts only 700 official members, more than 45,000 boomerangs have been sold in this country and the nationwide tournament circuit now includes more than 50 competitions between May and October.

Boomerang competitions usually consist of games designed to test the throwers' range, speed or strength. Some of the more basic events include "Accuracy", a 19th-century game whereby 'rangers attempt to land their throws as near as possible to the point of origin; and "Suicide," an exercise in chaos invented by Benjamin Ruhe in which dozens of 'rangers launch their boomerangs simultaneously and attempt to catch them. 'Rang collisions and progressively more difficult catches (such as behind-the-back or with the feet) are used to eliminate contestants.

Other events include "Doubling," where a thrower launches two boomerangs at once and attempts to catch them; and "Juggling," in which a 'ranger throws and catches two boomerangs alternately, keeping one in the air at all times. Barnaby Ruhe set the world juggling record in 1984 with 161 consecutive catches.

The Smithsonian had sponsored a boomerang workshop/tournament annually since 1969, but discontinued it in 1981 when the crowds got too large to handle.

And therein lies the hurdle to the sport's growth. Crowds and competition run counter to the very things that lure 'rangers to the sport -- open spaces and freedom from rules.

But boomerangers aren't complaining.

"It's a deeply personal little sport," says Benjamin Ruhe. "I think deep down inside, most boomerangers would just as soon keep it as their secret." NOT-SO-LONE 'RANGERS

The second annual night Korobari, which Benjamin Ruhe describes as "really poetry . . . beautiful to see," will include at least five four-man teams competing in such events as "accuracy," team relay, fast-catch, endurance (the most catches in five minutes) and "doubling." The competition, on the polo field in West Potomac Park near the Lincoln Memorial, will run from around 9 to around 11. The organizers caution against bringing small children or dogs. For more information, call Chuck Bernstain at 965-4230 or Benjamin Ruhe at 234-9208.

QUALITY BOOMERANGS -- range in cost from $6 to $30, depending on the material and craftsmanship. A wide range can be found at The Kite Site, 3101 M Street NW, Georgetown. 965-4230.

Specialized boomerangs can also be ordered from: Flying Trees Ltd., 4513 Randolph Rd., Wheaton, 933-6211; and from Benjamin Ruhe, Box 21182, Kalorama St. NW, Washington D.C. 20009.

One-year membershp in the USBA costs $10 and includes a quarterly newsletter, free entry in USBA tournaments and merchandise discounts. Write to: USBA, Box 2146, Lower Burrell, Pa. 15068.