KITES WON'T BE the only paper birds taking to the air this spring. For the next five weeks, paper planes will be descending on Seattle's Museum of Flight to meet the May 1 deadline for the Second Great International Paper Airplane Contest.

If you've longed for Sky King status ever since your first glider looped the loop in fifth grade homeroom and landed both of you in the principal's hangar, this may be just the right contest. Jointly sponsored by the National Air and Space Museum, Science 85 Magazine and the Museum of Flight, the contest is free, the rules are few and, unlike kite events, there are no strings attached.

Events and categories have been designed for almost everyone -- aeronautical professional, armchair expert, four-year-old or artist. Competition areas include time aloft, distance, aerobatics and aesthetics of design. Although each plane is restricted to one event, there's no limit to the number of planes a contestant may enter.

Eric McNett of Brunswick, Maine, has submitted one elaborately boxed paper airplane a week for the past seven weeks, positioning each plane in a network of styrofoam pillars to guard against en-route flattening. A fellow competitor has avoided the packaging problem altogether by simply mailing in his plane unboxed, with the proper postage affixed directly to the plane itself. Another contestant, Mark Lenard, has an all-or-nothing attitude: He's entered a paper airplane inscribed with the message "If it doesn't win first place, do the honorable thing." He has attached a match.

Entries have come from as far away as Yugoslavia and Ghana. A preliminary satellite contest is underway in South Africa, with the winner moving on to Seattle, and similar contests are taking place in West Virginia, Alaska and California. Elementary schools are depositing cartons filled with student-made paper planes and even corporations are getting into the act. Employees of the Seibu Corporation in Japan plan to enter approximately 800 planes, according to Ali Miller, the coordinator of special events at the Museum of Flight.

Nearly a thousand planes have been received so far, and the total is expected to exceed that of the First Great International Paper Airplane Contest held in New York City 18 years ago, when 11,851 entries arrived from 28 countries.

What's in it for the contestants? Fun -- certainly. Fame -- possibly.Fortune -- well, two out of three's not bad. First- place winners can expect a free trip, in a real airplane, to Seattle to receive their Bernoulli Medallions (named for Daniel Bernoulli, an 18th-century physicist who pioneered theories of air pressure and flow) and to fly their planes at a special ceremony. And the David Letterman Show may have the winners and their paper airplanes appear on Late Night.

But before you take off to buld your entry, here are a few rules to bear in mind:

* All planes must be made only of paper. Glue and cellophane tape may be used only for bonding purposes, not to add weight. Paper lamination and paper reinforcement are allowed.

* Your entry is your airplane, properly folded, with your name, address, phone number and any special throwing instructions written clearly on the plane. Also indicate which event you would like to enter (remember, only one event per plane) and whether you are in the professional, nonprofessional (an aeronautics engineer, say) or junior (under 14 years of age) category.

* Send entries, questions and requests for copies of the rules to: International Paper Airplane Contest, Museum of Flight, 9404 East Marginal Way South, Seattle, Washington 98108, 206/767-7373.

* Entries must be received by May 1. Elimination fly-offs are scheduled for May 21-24; the winners will be announced on May 28.