If we could do away with breathing, we might be a lot healthier.

Sure, the air outside at the moment is crisp and clean, washed by the snow and whooshed by the wind.

So try to remember to take a few deep breaths (if it's not too cold) when you're outside.

Because inside air may be a problem... downright lethal in some cases, right in your own office, right in your own house, right in that fancy restaurant.

People have lungs to perform a number of functions, the primary one being exchanging oxygen for carbon dioxide.

And lungs, being more exposed to the outside than anything else in the body (except the skin), have all sorts of sophisticated defense mechanisms.

Dr. Alfred Munzer, pulmonary specialist and director of critical care at Washington Adventist Hospital, likes to describe the human respiratory system in a two-minute anatomy lesson he calls "the gospel of the lung according to Munzer."

"The lung's defense mechanisms are really very fascinating," he says, "but even these can be overwhelmed when exposed to excessive amounts of noxious agents."

The system, as we all know, starts with the nose.

"It humidifies the air we breathe, filters gross particles and brings the air to body temperatures. But smokers bypass this mechanism... I tell patients that at least if they won't stop smoking they should try smoking through a nostril."

Other gross particles are filtered in the trachea, which subdivides into bronchi -- major air possages -- and keeps branching off into literally millions of tiny little air sacs called alveoli where the exchange of oxygen for carbon dioxide takes place.

The branching of the bronchi offers a defense in itself. But in addition, cells lining it include those secreting mucous and others with tiny, constantly waving hairs called cilia. "Anything that gets past the nose, past the bronchi network, can be trapped by the cilia and carried back out."

There are two distinct types of mucous in the passages -- one type traps particles for the cilia to send back. The other dissolves water-soluble gasses, some of which are indoor air pollutants. This mucous also contains antibodies which fight specific infections. Finally, in the alveoli themselves are found irregularly shaped mobile cells called macrophages. "They are scavenger cells attracted to foreign particles that get into the alveoli. They can ingest [these particles] and can kill bacterial organisms."

All of this is important to know to understand, for example, why people who smoke or are around other smokers tend to get more upper respiratory tract infections than others.

Tobacco smoke, and several other substances including ozone and alcohol, can damage these denizens of the last line of lung defense.

Says Munzer, "The insidious effects of indoor pollutants are not merely that they are direct agents to the respiratory tract, but that they also interfere with the defense mechanisms of the lung, making the lung more susceptible to other offending agents."

Munzer, past president of the D.C. Lung Association, was a participant at a recent lung association seminar on indoor pollution.

Tobacco smoke is still probably the chief culprit for smokers and non-smokers as well. New studies have indicted so-called side-stream smoke in respiratory ailments especially in children of smoking parents as well as in adults with other breathing problems -- allergies, asthma, cardiovascular problems for example.

But there were also discussions of other common pollutants at work place and at home, a situation exacerbated by efforts to conserve fuel and lower fuel costs.

Some of these were outlined by James Frazier, staff officer on a recent major report by the National Academy of Sciences on indoor pollution; by Joel Makower, author of Office Hazards: How Your Job Can Make You Sick; by Thomas Conry, a chemist with the Environmental Action Foundation, and James Repace, a specialist in indoor air pollution.

Breathing the air in poorly ventilated offices and many homes in "like everybody in the house taking a bath in the same water," says Makower. Everyone's germs are shared. Toxic gases and radiations, as well as fungi and molds, can come from building materials, synthetic materials, poorly maintained copying machines, old ventilation systems or new ones that are set down to conserve fuel. Asbestos fibers are ubiquitous in older buildings and fiberglass and other insulation can be irritating, if not as potentially deadly as asbestos.

Formaldehyde, which can cause dizziness, headaches, rashes and respiratory problems in the short run, and possibly even cancer in the long run, has become such a problem that a national organization devoted specifically to its victims has been formed. The group, called SUFFER -- for "Save Us From Formaldehyde Exposure Repercussions" -- keeps members alert to new uses for the chemical.

Formaldehyde is given off as a gas by many building materials, new flooring, paper products, fabric finishes and many other products. It is included in some products -- room deodorizers, for example -- because it deadens the sense of smell.

One of the problems brought out at the seminar: There is too little knowledge about what really constitutes pollution. Some people may be sensitive to certain substances at certain levels and others may have no reaction at higher levels. Certain mixtures of potential pollutants may cause significantly more harm than either alone in even greater quantities. One thing the report of the Academy of Science made clear was the need for much more research and much more education.

As Frasier says, "We need to relate exposure to health effects. We have to be able to say we see this effect with this exposure with this duration of time...."

Even when standards have been established for exposure limits to hazardous chemicals in the work-place, notes Frazier, they were set on the basis of a healthy 150-pound male worker. "We're talking about a different population when we talk about exposure in the home... infants, old people, pregnant women, the healthy, the sick."

Other potential home-pollution sources:

* Combustion -- unvented, or poorly vented gas stoves. Fires in fire places. Kerosene space heaters. The gases given off can cause eye irritation, respiratory diseases and even affect sensory perceptions.Children in homes with poorly vented gas stoves have more respiratory illnesses. When parents smoke as well, they are doubly at risk.

* Aerosol sprays. Any kind of any product produces particles that can get by or at least damage some of the lung's defenses.

* Pesticides. Many have been linked, at least indirectly, to cancers and cardiovascular diseases.

* Synthetics. Substances used to give plastic its flexibility, as in shower curtains, can give off gases whose effects have been too little studied, but are known to be hazardous under certain conditions.

* Hobby products. Artists' materials, glues and other products are chock full of toxic substances.

The speakers agreed that it is important to urge manufacturers to include all chemicals on labels, to remember to link illnesses and even vague distress to exposure to potential dangers at home and office and report symptoms to physicians.

Says Conry, who outlined hazards of the home, "People ask me how I get up in the morning. Sometimes I wonder."