MARYLAND SCIENCE CENTER, 601 Light Street, Baltimore. Pay parking available around the Inner Harbor. Open Tuesday through Thursday 10 to 5, Friday and Saturday 10 to 10, Sunday noon to 6. Adults: $2.50, children under 12: $1. Phone: 301/685-2370.

Red lights flash on the control panels. Kaleidoscopic images dance across the radar screens.

"Ready, go!" shouts a child from one of the three pilot seats.

"Uh-oh. I'm out of order," says his co-pilot.

"I'm going to the moon," decides the third pilot, flicking the switches, spinning the dials and moving around all the switchboard plugs that control the spaceship. It's a short trip, and the kids soon burst out, eager to try more of the hands-on activities that fill four stories at the Maryland Science Center in Baltimore.

"You better put on your oxygen masks before you come out here," advises the volunteer in the K.I.D.S. (Keys Into the Discovery of Science) room, designed especially for four-to seven-year-olds.

But the kids are already reacclimated and into something else. A little girl fills a can hanging over a table with sand, then gives the can a push. The sand falls on the table, making a design.

"It looks like a snail," says the volunteer. On the floor, younger kids are scribbling on paper with crayons, then holding their works under a light that makes the art look phosphorescent.

Upstairs, older kids and adults who didn't get electronic games for Christmas are playing games with computers called Merlin and the Little Professor. A display next to each game shows how small the computer's brain is, but some people lose nevertheless. Others take on another computer in an academic contest.

"Welcome to the lunar quiz," prints the computer. "What is the difference between moons and satellites?"

A teenager chooses answer No. 3, and the computer pats him on the back.

"That's right," it prints out. "The terms are interchangeable."

Other kids pit their wits against those of other real live humans in a game of electronic tick-tack-toe based on the metric system. Instead of Xs and Os there are red lights and blue lights and to fill in a square with your color you have to get the right answer to such questions as "True or false: A high diving board is three meters above the swimming pool?"

Another display shines lights down on you and claims it can measure your height by measuring your shadow.

"Hey, mom, am I five feet?" asks a boy who isn't quite sure it really works.

On the demonstration stage, a woman is talking about physical reactions and asks the audience what they are.

"When the way it looks changes" ventures a kid, who is told yes but that in a physical reaction -- as opposed to a chemical reaction -- you usually can bring back the materials you started with. This physical reactiion, she explains, will be between calcium acetate and denatured alcohol.

"Is that the kind you put on with cotton?" asks the same kid. "And can I stand here on the stage?"

"No, that's isopropyl alcohol," replies the woman. "And you can stand there but don't get any closer."

She measures out 100 milliliters of alcohol and 40 milliliters of calcium acetate and mixes them together and gets something the kid on the stage of the stage says looks like water.

"But it isn't," she warns. "And if you don't know what something is, don't drink it or play around with it."

She attempts to pour the concoction from the beaker, but finds the mixture has changed.

"It's not liquid anymore," she says. "I can't pour it. But it's not solid because I can put a stick in it. It's something in between -- a colloid. Jello and vanilla pudding are also colloids, and the next time you make a mud pie, that's a colloid, too."

But can she change it back again? She holds the beaker upside down and squeezes the colloid. Drops of alcohol drip into another beaker, proving it was a physical reaction.

At an exhibit on temperature, kids are causing their own reactions by putting a finger on a heat sensor and raising the temperature from 30 degrees to 31 degrees -- Celsius, of course. Right next door, kids touch a series of buttons that show them what it feels like from 0 degrees right up to 70 degrees.

"I told you it was hot. You had to touch the hot one," says a mother to a boy who didn't touch the 70 button gingerly enough.

Two other kids are taking a scientific test of strength, squeezing two levers together and finding the result in newtons. A newton, explains the display, is the amount of force needed to accelerate one kilogram from rest to a speed of one meter per second in the time of one second.

"I got 12," boasts a little girl.

Other levers are pulled to illustrate theories about how the continents got that way. A squeeze brings South America very close to Africa.

"Does it seem likely that the two continents were once joined?" asks the exhibit.

A giant crab introduces visitors to an exhibit on the Chesapeake Bay. The crab moves its claws back and forth and words flash on a screen.

"I welcome you two-legged creatures to my slice of Maryland," a mother reads.

"Is it real?" asks a kid, suspecting that the welcome may be a trick. In another part of the museum kids find gentler creatures -- gerbils, huddling together.

"Look, the baby went under the ground," say the kids, excitedly. "Look, he's trying to get in so he can sleep with everybody."

Back in metric land, the youngsters are getting a feel for the metric system by lifting suitcases marked 5, 10, and 20 kilograms. Others are weighing keys, pennies and pencils. When the loudspeaker announces a demonstration of inertia, the kids drop the suitcases and scales and flock to the stage to hear about Sir Issac Newton.

"He didn't bake cookies; he wasn't that Newton," explains the woman on the stage. Instead he cooked up the law of inertia which, she explains, means that things tend to stay put, even when a tablecloth is pulled out from under them.

"This is at rest," she explains, placing a cup and saucer on the tablecloth. "It has inertia, or weight."

She adds three more cups and saucers and then remembers that she forgot the tea.

"I didn't have time to make it, so I'll use plain water," she says filling the cups and piling one cup and sacuer on top of the other. "So you feel secure?" she asks the people sitting right near the stage. "Do you have raincoats?"

With an abracadabra, she yanks the cloth, and the cups stay put.

"The more weight something has, the most inertia it has," she explains. "So I was really helping things by filling the cups and putting one on top of the other, even though it looked more dangerous."

At the nutrition machine, people are telling all to a computer. Not only their age, sex and weight but what they eat for breakfast, lunch and dinner. In return, the computer tells them what more they ought to eat to have a balanced diet.

"Your diet shows serious nutritional defects," the computer tells a seven-year-old. "Please wait while I suggest some foods to supplement your choices."

The machine suggest beef potpie, cheese omelets, broccoli and oysters.

"Ugh!" says the kid and walks away.