They were wonderful parents. Everybody said so. Made sure the kids had all the right shots at the right times. Made sure the kids ate only the right foods. Read to them. Sang to them. Made sure they brushed with fluoride toothpaste. Talked with them. Played with them. Cuddled them. Comforted them. Took them for regular physicals.

Nevertheless, they may have sliced 10 years, maybe more, off their life spans and almost certainly contributed to making them sick babies.

Because wonderful as these parents were, they smoked.

And they turned their youngsters into what doctors are calling "involuntary smokers," or victims of "sidstream" smoke, or "secondhand" smokers. Or, you might say, secondhand children.

New studies all over the world are beginning to document the damage smokers do, not just to themselves, but to those who must breathe the air their smoking habits pollute.

Especially, tests are pointing up the damage done to the lungs of infants and children in homes where there are smokers.

What would you do, smoking parent, if someone forced your baby to smoke cigarettes?

Well, according to Dr. Alfred Munzer, president of the D.C. Lung Association and a lung specialist at Washington Adventist Hospital, that's just what you are doing. "Parents," he said recently, "really should be careful about smoking around their children. Any parent who suspected that someone was knowingly making their child smoke five cigarettes a day would probably be very unhappy...." Yet, he noted, "estimates are that the effect on young children of parental smoking is about the same as if the child smoked three to five cigarettes a day."

Recent studies in Israel have established a relationship between the incidence of pneumonia and bronchitis in the first year of life and the smoking habits of the patents. The studies also show that the greater the number of cigarettes smoked in the home, the greater the incidence of respiratory infections in the infants.

At Wayne State University in Detroit a research team found that respiratory diseases in young children increased drastically when the parents smoked and another study at the Mayo Clinic found that parental smoking could trigger asthma attacks in susceptible children.

It used to be thought, Dr. Munzer said, that lung growth stopped early. In fact, it has been determined that the lungs and the bronchi take much longer to develop and "any early injury is going to be magnified later in life."

"Next to smoking," he said, "the most significant risk factor in the development of chronic lung disease (emphysema, asthma, bronchitis, for example) is a history of childhood respiratory infections. And children brought up in homes where parents smoke are likely to contract two to three times more deep chest infections than children in homes where there are no smokers."

The effects on children are most striking, but sidestream smoke can have deleterious effects on almost anyone who is subjected to it.

Dr. Munzer calls it "the principal source of indoor pollution."

It is unpleasant, inelegant and smelly, of course, but it is also:

The sole source of arsenic in the atmosphere.

A major source of carbon monoxide, hydrogen cyanide, nitrogen dioxide and nicotine in the air.

A major source of other noxious compounds some of which are known to cause cancer.

(It's not so hot for pets either, by the way. Laboratory tests on animals - performed primarily, of course, for the eventual implications for humans - found that mice exposed to secondhand smoke got bronchitis, rats got lung tumors, rabbits got emphysema, and dogs suffered a breakdown in lung tissues when exposed to a secondhand cigarette smoke 10 times a week for a year.)

Besides children, secondhand smoke is particularly dangerous to people with other diseases, especially heart or lung problems. Although it has not been proven that exposure to secondhand smoke will by itself cause cancer, cigarette smoke - both that exhaled by smokers and that which comes from the burning end of the cigarette - is positively loaded with carbon monoxide.

Carbon monoxide displaces oxygen in the blood's hemoglobin. In a person with coronary artery disease, Dr. Munzer said, the heart is always on the border of not getting enough oxygen anyway. The carbon monoxide from somebody else's cigarette has been known to provoke angina or more serious heart attacks in such persons.

Asthmatics, too, are already burdened by atmospheric pollutants from other sources and the sidestream smoke can push them into bronchial asthma attacks or exacerbate diseases like emphysema.

Other health problems associated with involuntary smoking include eye irritations, especially for contact lens wearers, worsening of the effects of hay fever and, in a few people genuinely allergic to tobacco smoke, serious air-passage obstruction with wheezing and other allergic symptoms.

Dr. Munzer applauds clear-air laws and anti-smoking ordinances similar to those now in force in the District and parts of Maryland. He urges nonsmokers to be more assettive, particularly with today's cutdown on air conditioning - and therefore ventilation - in offices. And he is especially concerned about the possibility that "the greatest danger is in our homes," where "you can't legislate."

He sighed and observed that if the outdoor clean-air regulations were to be applied indoors, tobacco smoke would make violators of us all. CAPTION: Picture, no caption