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One of the chemists developing synthetic pheromones to lure insect pests to their destruction is Dr. Donald S. Matteson of Washington State University at Pullman. Most of these pheromones must consist of only one chiral twin to work; the use of the wrong twin or of an equal mixture of both twins may not work at all.

Dr. Matteson's group has synthesized four insect pheromones that are identical in their handedness to the natural ones. To do so, they used natural handed molecules derived from sources like pine trees to create templates for starting out the pheromone molecules with the correct handedness. Don't Drink Looking-Glass Milk

In Lewis Carroll's tale "Through the Looking Glass," Alice wonders whether "looking-glass milk" on the other side of the mirror would be fit to drink. Dr. Matteson answers that it would not, because biologically active molecules in the milk, notably sugars and proteins, would have the wrong handedness for Alice to digest, unless her own chemistry were converted to its mirror image by passing through the looking glass.

But the very indigestibility of wrong-handed compounds may have its uses. The sugars that are used by the body, for example, are right-handed; left-handed sugars are indigestible. This fact is the basis of at least one patent for a sweetener made from a left-handed sugar that supposedly is non-fattening.

Wrong-handedness is also a possible basis for the development of new antibiotic drugs.

Amino acids, the building blocks from which proteins and the other chemical ingredients of life are assembled, are chiral molecules that can take either left-handed or right-handed form. But with the exception of glycine, which has no handedness, the amino acids in almost all living things are exclusively left-handed.

A bizarre exception to the left-handed rule is a microorganism called Bacillus licheniformis, which makes the protein in its cell wall from right-handed amino acids. Scientists believe the organism does this to make itself indigestible to the killer cell phagocytes in animal blood that would normally attack it.

Drug companies study the use of molecular wrong-handedness to poison disease-causing bacteria without poisoning their human hosts. Springing a Chemical Trap

Dr. Reider explained that although human beings and other animals can metabolize only the left-handed enantiomer of the amino acid alanine, bacteria contain an enzyme capable of converting right-handed alanine to the digestible left-handed variety. The strategy of a drug designer might therefore be to attach a suitable poison to right-handed alanine molecules. Because the human body could not metabolize the right-handed compound, it would not be affected by the poisonous booby trap. But a bacterium could devour and metabolize the right-handed compound, thus poisoning itself.

Although the boom in chirally pure substances began only recently, the realization that mirror-image twins behave differently dates to the early 19th century. In 1844, the German chemist Eilhardt Mitscherlich discovered that although a solution of commercial tartaric acid in water twists a beam of polarized light to the right, a solution containing a related compound, sodium ammonium paratartrate, has no effect on the light beam.

In 1848, Louis Pasteur discovered that the paratartrate actually consists of two different kinds of crystals that can be clearly discerned under a microscope. Using tweezers, he separated the crystals and dissolved them in separate solutions. Passing polarized light through each of the solutions, he found that one solution twisted the light to the right and the other an equal angle to the left. The reason the unseparated paratartrate solution had no effect on the polarized light beam, Pasteur realized, was that the light-twisting effects of its two enantiomers canceled each other out. The reason the constituents behave oppositely is that their molecules are mirror images of each other.

Many methods are used today to synthesize or separate enantiomers, but some still involve variations of Pasteur's approach.

With the new emphasis on chiral chemistry, government officials in Europe, Japan and the United States wonder whether there is a need for regulations that address the handedness of drugs.

Some chemists believe too little money is available for research to determine the pharmacological differences between enantiomer twins. Work on Anesthetics

Dr. Jerrold Meinwald of Cornell University and his associates have devised chemical methods for separating the enantiomer pairs in three common anesthetics, halothane, enflurane and isoflurane. Their success with these technically difficult separations means, in principle, that enantiomers could be produced in sufficient quantity to conduct clinical trials. Because small amounts of anesthetic are metabolized by patients, it would be useful to determine any differences in the toxicity of their enantiomers, Dr. Meinwald said.

"Scientists really don't know much about how anesthetics work," he said, "and study of their enantiomers might shed light on this question, while possibly helping to eliminate the small risk of dangerous side effects that some anesthetics have."

But funds are lacking for large-scale animal tests of anesthetic enantiomers, he said, and without these, further research is stymied.

The pharmaceutical industry has counseled caution in regulations concerning the handedness of drugs. The Pharmaceutical Manufacturers Association said last year that each case should be decided on its merits by the manufacturer.

The Federal Food and Drug Administration essentially agrees.

Dr. Judi Weissinger, assistant director of the agency, said, "The F.D.A. is not going to insist on some inflexible checklist" of analyses and trials of chiral drugs. Instead, she said, the agency would continue to alert manufacturers to prudent guidelines.

Underlying all chiral chemistry is the fundamental question of why the amino acids making up virtually all living things are exclusively left-handed.

The fact that they share the same handedness is easily explained. "To fit biological molecules together properly, you must use molecules with the same chirality. The helical DNA molecule, for instance, could not be assembled from a mixture of enantiomers. The components must all have the same handedness," said Dr. Eliel, the University of North Carolina chemist.

But why are they left-handed and not right-handed?

Many scientists believe that the direction of handedness resulted from the flip of a chemical coin, and that once the pattern was established, subsequent molecular development had to follow suit.

But some theorists say they believe that left-handed biology may have its origin in the "weak" nuclear force. This force, which drives certain types of radioactive decay, is not precisely even-handed but has a slight left-handed bias. A group of British investigators found in 1985 that the mixing of the weak force with the electromagnetic force would slightly favor the formation of left-handed amino acids.

But right-handed and left-handed amino acids appear to exist in roughly equal quantities in meteorites that hit the earth. And an analysis published last month in Physics Today by three Soviet scientists, Vladik A. Avetisov, Vitalii I. Goldanskii and Vladimir V. Kuzmin, argued that the weak force is far too weak to have determined the direction of biological handedness.

Scientists may never know what gave life its chiral bias, but on one point they agree: without an initial spin, no one would be here thinking about it.

Diagrams: "On the Other Hand . . ." Molecules that exist as mirror-image twins often have very different properties. The left-handed and right-handed versions of the carvone molecule have the same composition -- 10 carbon atoms, 14 hydrogens and one oxygen -- and their structures are mirror images. The molecule carvone, C10H14O. Left-handed carvone, at left, has the odor of spearmint. Its right-handed twin, at right, has the odor of caraway and dill seeds. (Source: "Molecules," P. W. Atkins (Scientific American Library) (pg. C1) "The Importance Of Being Handed" Chiral chemicals are handed in the same way that hands themselves are either left or right. The direction of a molecule's handedness determines the types of interaction a chemical can have with other chemicals. Atlanine This amino acid is one of the building blocks of life. Animals can use only the left-handed form. Bacteria can use the right-handed form by converting it to left-handed alanine. Thalidomide This sedative deformed babies born to women who took it. Some scientists say only one form may have been at fault, while the twin may have been harmless. (Source: "Molecules," Atkins (Scientific American Library) (pg. C8)