THE CRAFT and science of genetic engineering seem anything but simple. They entail a complex sequence of microscopic procedures to remove specific double-helix strands of deoxyribonucleic acid (DNA) from an organism's cell nucleus and replace them with pieces of DNA from another source. Scientists make the swap by using chemicals called restriction enzymes, which break the bonds between linked sections of the original organism's DNA. The broken spaces are then exposed to "donor" DNA strands that have similar linking mechanisms; the donor strands fill the empty spaces and the bonds are re-sealed using repair enzymes.

The process can be used to modify a cell's chromosomes directly or to re-shape a plasmid (one of the dozens of circular DNA molecules that exist and replicate themselves outside a cell's chromosomes). In either case, the cell uses the new DNA coding to reproduce itself, resulting in a genetically altered organism.

When researchers first used these procedures, everything had to be done "by hand" experiment by experiment. But since the early '70s, the chemicals and techniques required for genetic engineering have become standardized, simplified and widely available.

Just for fun and as an intellectual exercise, Dr. Robert Goodman, vice president of research and development at Calgene, a leading plant biotechnology company in Davis, Calif., agreed to suggest the hypothetical outlines of a simple biotech engineering kit which could cost less than $100.

Imagine, Goodman says, that you want to genetically engineer tomatoes to glow in the dark. Within three years, he believes, the project could be accomplished by a 4-H Club or sophisticated gardener.

With the right bacteria, a few plant hormones, a microwave oven and a lot of patience, this kit could yield a crop of tomatoes you could see in the dark because the plants have been modified to contain luciferase -- the oxidyzing enzyme that helps produce light in fireflies and other organisms.

The microbial tool that genetic engineers use to create "transgenic" plants today is Agrobacterium tumefaciens (literally, "tumor-making"), a naturally occurring bacterium that causes a plant to become tumorous by mixing its genetic code with the plant's.

"We don't quite understand exactly how it does what it does," says Goodman, "but it works."

The idea is to deploy the agrobacterium by taking away its tumor-making genes but keeping its DNA-transfer ability. That way, the bacterium can transfer a genetic message without killing the tomato plant. In a commercial environment, scientists would have to doctor the bacterium so that it contained the desired genetic coding. But for the purposes of this imaginary biotech kit, the agrobacterium comes freeze-dried with the luciferase gene already built in.

Mutants du Jour Ingredients: Agrobacterium tumefaciens (with luciferase); agar; petri dishes; Clorox; various salts; carbenecillin; tomato seeds; auxin; kinetin; sugars; sterile soil; pipettes; graduated cylinder.

Directions:

1. Dip a few tomato seeds in Clorox; rinse in sterile water; place on filter paper in petri dishes and let germinate in the dark.

2. Grow the agrobacteria in a nutrient overnight.

3. Cut the small leaves from the seeds at a 45-degree angle with the sterile scalpel.

4. Dip the cut leaves in the agrobacterium and remove. Place them on filter paper and lay the paper over a base of nutrient agar. Wait about 36 hours.

5. Create a growth medium to regenerate the tissue: Mix agar with some salts, kanamycin (kills the non-transformed parts of the tissue), carbenecillin (kills the agrobacterium) and a couple of plant-growth hormones (auxin and kinetin). Place in petri dish. Zap with microwave to solidify the agar. Plant the resulting material and wait one month.

6. Prepare another growth medium for the roots. (Same as step 5, but skip the kinetin.) Zap in microwave.

7. Very carefully transfer shoots to new medium. Wait one month.

8. Transfer to sterile soil and keep under light. Then re-pot. (NOTE: Make sure to observe National Institutes of Health containment guidelines about release of genetically engineered organisms into the environment.)

9. Sit out on the porch and watch your crop light up. "You can get thousands of these transgenic tomatoes," says Goodman.