The trouble with bugs -- like the common head louse -- is their "genetic intelligence."

In the chemical battle against their ever-increasing inroads, the lice (and the "nits," their eggs) are winning. Estimates range from 6 to 10 million infested heads a year -- or something like one-twentieth of us.

Not only are the ugly critters quickly developing strains resistant to insecticides -- because of their short lifespans -- but the chemicals themselves now are being seen as potentially harmful to human users.

Lindane is the chief active ingredient in the anti-louse shampoo "Kwell," and other prescription remedies.

The prestigious Medical Letter on Drugs notes that lindane "can be absorbed, however, and convulsions have followed the treatment of scabies when too much was applied to the whole body, or for too long." A ban of lindane has been proposed which would limit its use as an insecticide and require a prescription for cat and dog flea collars which contain it. But Dr. Fred McIlreath, spokesman for Kwell's manufacturer, says that their tests have shown "extremely small" absorption of lindane from shampooing. When directions are followed, the manufacturer feels it is safe.

The chemicals in non-prescription preparations such as "RID," are irritating to eyes and mucous membranes and have produced some allergic reaction, but are probably less hazardous than lindane, says The Medical Letter.

One of the problems with chemical control agents has been thier inadvertent misuse by panicked parents. Instructions suggest use no more than once in 24 hours. However, when it seems not to work, it is used again and again, in a feverish -- and possibly dangerous -- attempt to banish the nits.

The pediculus humanus capitis has been around probably as long as we have. Nits have been found on the heads of Egyptian mummies. They're unpleasant, of course, but a lot of misconceptions have made them seem worse then they are:

They are NOT connected with poor hygiene, or "dirtiness," or even low economic status. Nobody's immune.

Blacks are NOT especially protected from infestation, although head lice tend to prefer straight hair to curly for egg laying.

Francis Lewis of the D.C. Health Department speculates that the use of hot combs and hair straighteners and shorter hair styles seemed to protect black children years ago. (Lice are very heat-sensitive and tend to shun light.) But the "bush and other longer, natural styles may account for the increase in infestation among black children. (The frequent use of warm blow dryers can help prevent it.)

Head lice are cousins of body lice, but differ significantly in their offensiveness.

Body lice, but not head lice, have been associated with typhus and other illnesses. Body lice lay their eggs inclothing and may be transmitted easily from one person to another.Shared hats and combs, of course, do a good job of transmitting had lice, as does the head-to-head contact to which tumbling youngsters are prone. (Children at school should have separate and specific places to keep their coats and hats.)

But the future is not all bleak.

A small organization called the Technical Assistance Center for Urban Integrated Pest Management, part of the John Muir Institute for Environmental Studies Inc., is taking a new approach to the problem with possibly the oldest technique of all: combing.

It is not, of course, quite that simple. The combing -- with a special metal comb while the hair is wet and sudsy -- must be done persistently, hair-by-painstakingly-hair.

One comb is manufactured especially for use against nits by the Johnson Manufacturing Corp., in Boonton, N.J. However, so-called "flea combs," designed for cats and available at pet stores, are also suitable. The teeth shold be only 1 millimeter apart.

William and Helga Olkowski, co-directors of the Pest Management group, and their East Coast representative Kevin Hackett, are preparing a pilot project of interested (and infested) volunteers to test their thesis that the use of chemicals can be greatly reduced, even while control is improved.

They do not necessarily recommend use of no chemicals, but urge that they be limited in amount, and only in cases where really needed. For example, notes Hackett, who has a Ph.D. in insect pathology, "If nits are found more than a quarter of an inch from the scalp, chances are they have already hatched."

The louse lays the egg as close to the scalp as possible and they hatch in about a week; hair grows about a quarter of an inch a week. Chemicals, therefore, are ineffective.

Spraying around the house and boiling sheets , clothes, pillows cases is probably not a useful exercise for preventing reinfestation, although these things should be washed, or dry cleaned, and the house should be thoroughly vacuumed. Lice can live off the human head only for about two days.