The boys had been looking forward to the fishing trip for a month, but the when the day arrived it was to wet and windy to be messing about in boats.

Told we were going to a museum instead, Mark, eight, grumped. Neighbor Andrew, six, who is a polite person, merely moped. Museums to them are places where big people get in your way and they won't let you touch any of the neat stuff. I didn't tell them we were going to the one museum in Federal City that seems designed for little boys.

They began to perk up as we rolled through the arched gateway of Washington Navy Yard at Ninth and M Streets SE and they saw all the people in uniform. When we parked by the submarine conning tower in front of the Navy Memorial Museum they began to rattle around in the van like jumping beans.

"It sank right in the street!" Andrew said.

"Don't be silly," Mark admonished him. "It blew up."

They went capering off into the outdoor display area, which is packed with huge guns and sinister machines and other vasty articles of the sailor's trade. The park is in the process of restoration, and the litter and craters add verisimilitude.

Told they could touch it all, and climb on some of it, they ran riot for half an hour before beginning to lose stream. Andrew tiptoed up to a bronze ship's screw as tall and heavy as his house and stood awhile in thought.

"Where's the rest of the plane?" he asked.

"That's a propeller from a ship. It had three more just like it. Some have more." Andrew grinned. He may have been born yesterday, but he knows when he's being had. The same large person had only moments before told him that the rocket at the far end of the park was designed to be fired from a submarine under the water.

The boys protested when told to go inside, until they discovered they were being herded into heaven. More guns. Guns you can climb on, and that swing around when you crank the big brass wheels. They ack-acked each other to rags, providing bolder and bolder sound effects as they came to realize that nobody was going to tell them to be quiet, and that in fact they had the whole place to themselves.

That's the other great thing about the Navy Museum. The Navy Yard is off the tourist track, and most Washingtonians don't seem to realize it's open to the public. Even on summer weekends the place is seldom crowded. Besides permissiveness it has the charm of clutter; the museum is the Navy's attic, and the placement of some exhibits suggest they were left where they happened to be when the staff went off to lunch.

Everywhere the boys turned they found new marvels: ship models that would fit in a bathtub, and others that would hardly fit in a swimming pool; swords and rifles; submarine periscopes through which they could inspect boats plowing the fertile Anacostia River; a stainless-steel bathyscaph with hatch invitingly open.

"Can we get in it?" Mark asked.

"It doesn't say you can't."

They whooped themselves hoarse to hear the musical instant echoes inside the giant sphere, and rolled around in helpless laughter as the large person squeezed himself in.

Hunger finally overcame them. On the way out they passed a couple of World War II-model atomic bombs. They asked if they could touch them and were told yes.But they didn't.

Outside the museum was a moribund pigeon, fluttering in a drainage ditch. Lifted out, he tumbled back in. They boys wanted to do something for the poor verminous creature, and ere not satisfied by the philosophical ramblings of the large person. And so it goes.

Lunch was another delight. There is nothing outside Building 184 (corner of Parsons Avenue and O Street) to tell the uninitiated they may enter and eat, but when you find it the food is cheap and good. The boys were much taken by all the uniforms. Contemplating some enlistment brochures at the table, Andrew announced that when he grows up he's going to be a lady Marine. Mark couldn't talk him out of it.

Just up the street (Building 58) is the Marine Museum, which is strictly a no-touch affair but with superb exhibits the boys found entrancing. Children under four feet tall must be lifted to see into many of the display cases,there being no stools provided.

Outside, to draw off their last reserves of energy, was the parade ground, ringed with cannon and containing an anchor as big as the Ritz. Told it was from an aircraft carier, Andrew wasn't fooled. He knew perfectly well it was a fishhook for whales.

NAVY MEMORIAL MUSEUM -- At Washington Navy Yard, Ninth and M Streets SE. Open weekdays 9 to 4, weekends 10 to 5.; MARINE CORPS MUSEUM -- At the Navy Yard. Weekdays and Saturday 10 to 4, Sunday 12 to 5.; COMBAT ART GALLERY -- Near Navy Museum; allegedly open weekdays 9 to 4, but don't count on it.