Lay in the supply of Kleenex, aspirin and chicken soup and fire up the vaporizer. It's virus time.

Rhinoviri, parainfluenza, respiratory syncytial virus - RVS to those who know it - tiny "bugs" one and all, as predictable as the seasons, as inexplicable as the weather, and as unpleasant as the worst of both.

All over the Washington area adults are sniffling and children are hacking and there is very little that can be done for either group.

While bacterial disease can be cured with antibiotics, very few viral diseases can be cured with drugs. There are vaccines to prevent infection by some viruses, such as those that cause polio, mumps and measles, but once a patient catches the diseases, all he can do is treat the symptoms.

For the past 20 years researchers at Children's Hospital National Medical Center have been plotting the seasonal course of the various viruses that show up in children.

"We're concerned with whether there's anything in the way of a pattern, predictability," said Dr. Robert H. Parrott, a virologist who is director of the hospital.

By following the illnesses for a number of years the researchers have been able to determine, for example, that parainfluenza 1 will strike every fail and cause an epidemic among 13-to 36-month-old children. Every other year parainfluenza 2, a similar "bug," will sweep through children of the same age.

"The first infection with some of these makes you pretty sick," said Parrott, "and many bring you into the hospital. With repeat infections you may not get as sick or you may get a minor illness."

In young children parainfluenza, which is present in the community now, "ofthen present itself as croup, so the clinical and epidemiological hint is that there's croup around."

Croup actually is an inflammation of, and swelling around the larnyx area of the throat, and is characterized by the fierce, barking cough that is all too familar to the parents of young children.

Croup can be extremely serious, because it can completely close off the airway, and may necessitate a surgical procedure to allow the insertion of a tube so the child can breathe. Most croup can be handled at home, however, but Parrott advises that if the coughing gets heavy, the child shoul be taken to a hospital.

The same virus may cause "a slight croup or a cold in older children," said Parrott, and adults in the family may have a cold-like illness.

"It's also possible that type of illness in adults may be caused by a virus that tends not to affect children an awful lot, the so-called rhinoviruses, and there're over 100 of them. They are the common cold viruses."

No one knows why the various viruses appear when they do, only that they do appear like clockwork year after year.

"There's no reason to believe" they spend their off-season in animals, said Parrott, so "one would have to believe ther're lingering around in some people; that's the best bet."

They may be brought out either by "the weather conditions or the relative susceptibility of the community," he said.

One of the probable factors in the fall outbreaks of viruses, said Parrott, is the return of children to schools where they can sneeze on each other and pass the viruses around.

Another factor, he said, is our tendency to spend more time indoors, in close contact with each other in colder weather, which also helps spread the viruses.

The next major virus likely to strike the younger population is the respiratory syncytial virus, or RSV. "I think we had our first isolate of the year last week," said Parrott, whose charts and graphs indicate that virus, which is the major cause of penumonia in young children, will peak in December of January.

And the flu season hasn't even begun.