THE WASHINGTON International Boat Show, originally launched in 1962 with 15 exhibitors, 15 boats and 36,000 square feet of display space, opens its doors at the D.C. Armory for the 16th straight year Saturday with more than 100 exhibitors, 500 boats and great collections of motors, hardware, accessories, clothing and other nautical miscellany.

The Armory's 140,000 square feet of space will nearly be swamped.

"The place will be jammed," said June Campbell, the show's coproducer. "We could just about use another armory. It would take almost that much space to satisfy the 30 exhibitors we had to turn away and the additional space wanted by the exhibitors already in the show. We are thinking that maybe next year we should have separate shows - one for sail, one for power.

Ironically, Campbell's partner in this year's effort has achieved substantial success in apparent competition with the show in the Armory. Peter Carroll has been putting on in-the-water boat shows in Annapolis since 1970 and admits that they hurt attendance at the winter show in the city.

"Now that I have an interest in this show," Carroll said, "you can understand that I tend to regard the Annapolis shows and the Washington show as complementary rather than competitive. And I think they are, because they give the local marine industry two shots at the prospective boat buyer.

"This year in particular the Armory show should do well, because people will come to look at things that will help erase the memory of our awful winter. In any event, the Armory show continues to be very popular with the exhibitors."

Indeed, most of the original 1962 exhibitors return year after year.The Washington Marine Co., for example, assembles some 20 boats and a mini store in the same area it has used from the beginning.

"We stock a cross-section of the items we carry in the main store," said president Bob Stickell, "with particular emphasis on the new and unusual. This year we're showing the Crooked Island Cat for the first time."

The Cat is 18 3/4 feet long, 9-feet-4 wide and draws 17 inches. Ten passengers should fit into it easily or it can carry more than a ton of cargo. While it is not an especially pretty vessel, it will appeal to those who want something functional for fishing, crabbing or lobstering.

Its 11 h.p. diesel engine only produces a speed of six m.p.h., but it can't be accused of wasting fuel. According to Stickell "it can run all day long on less than a gallon."

The boat's unusual safety feature is something called a "safety return rudder." Let go the tiller and the boat automatically turns in circles. The show price is about $9,000.

Backyard Boats of Alexandria will display two new sailboats. The Harpoon 5.2 (its length in meters) is the first sailboat put out by the company that makes the Boston Whaler. Superficially, it appears to be just another little day-sailor sloop, scores of which are already on the market. According to Backyard sales manager Bill Sharp, however, there is nothing superficial about it.

"There are absolutely no compromises in its construction and so what you get is super high quality. It costs $3,500 - which is about $1,500 more than some boats of the same length - but for those who want the best this is it."

Backyard will also show the new Hobie 18 catamaran, a craft substantially different from the Hobie 12s, 14s and 16s already on the market. All those have asymetrical hulls, don't use dagger boards and can be sailed in comparatively shallow water. While all are successful and popular, Sharp says their peculiar design reduces their efficiency and speed.

The Hobie 18 has symmetrical hulls, dagger boards, draws 2 1/2 feet and is a true racing machine, something on the order of the Olympic-class Tornado.

"It's really fast," Sharp said. "It should do 27 m.p.h. in a 22-knot wind." Boat show price: $2,875, without a trailer.

An even bigger catamaran - the Stiletto 27 - will be offered by Dockside Yacht Sales of Annapolis. A rounded canopy has been moulded into each hull and the combination somehow suggests two P-51 fighter planes. The canopies serve as seats and also provide access to seven-foot double berths in the hulls. Galley and head (both optional) give the boat a genuine cruise capability, though one should not expect the creature comforts of a monohull of the same size.

Since it's supposed to do better than 22 m.p.h. it will, of course, leave a same-size monohull behind in a hurry. A ingenious telescoping system permits the 14-foot beam to be reduced to less than 8 feet if the boat has to be trailered. The show price is about $13,000.

Because the ceiling precludes sailboats, most of the Armory's lower deck will be devoted to power boats. Certainly among the most exciting will be the $18,000 racing hydroplane shown by Precision Marine of Bladensburg, a low, sleek, wicked-looking job made especially flashy by various shades of vivid yellow paint.

Dealers at the show are offering free chances to boats - the most valuable a 9 1/2-foot Seafire ski boat worth $1,295 and put up by American Houseboating of the Ft. Washington Marina near Oxon Hill. Producers Campbell and Carroll will give away a sailboat - "we're not sure yet about the model, though it will be in the $1,000 range.

"We're also giving away something on family night, which is Tuesday. Kids 12 and under accompanied by an adult get in free."

Carroll said this year's show won't have a single "queen," a title boat show entrepeneurs habitually bestow on the largest craft on display.

"The marine industry is tending to get away from the emphasis on bigness. The Chesapeake Bay is so crowded now that even finding a boat slip is difficult. And slips are costly. One way to cope is to use smaller, trailerable boats - boats that can be put into and taken out of water practically anywhere. That kind of boat can save a lot of slip rent."

Tickets at the Armory box office will be priced at $3.50 for adults and $1.75 for children 12 and under. Each exhibitor, however, will be offering reduced-rate ticket through tomorrow. The 3.50 adult ticket will sell for $2.50; the $1.75 children's ticket for $1.50.

"This is something the dealers wanted," said Carroll. "If you go around on tickets and also probably get a preview on what he'll be showing at the show."

Parking lots adjoining the Armory can now handle up to 12,000 cars.

"Most of the Metro mess has been cleaned up," Carroll said. "The parking lots are fenced in and patroled by police. Snow, if there is any, will be removed quickly." Parking is $2, but the show's newspaper ads will include a coupon that cuts that to $1.50.

Show hours are 1 to 10 p.m. Feb. 19 through Feb. 21, 5 to 10 p.m. Feb. 22 through Feb. 25; 1 to 10 p.m. Feb. 26 and 1 to 8 p.m. Feb. 27.