With the advent of the age of antibiotics, the urgency for removing tonsils and adenoids in young children was minimized and the operation was performed less and less.

New research findings suggest there are indeed indications -- sometimes strong ones -- for one or both operations.

Says Dr. Kenneth M. Grundfast, chairman of Otolaryngology at Children's Hospital National Medical Center: "Each individual child has to be assessed by someone aware of current research that indicates that excessively large tonsils and adenoids can cause partial but significant airway obstruction, can lead to abnormalities of facial growth and, when very severe, can put a strain on the heart."

The operations now are considered separately and the indications, most specialists agree, are not the same. They also are beginning to agree, however, that chronic snoring and snorting caused by enlarged tonsils and adenoids in a child is a good indicator for removing both in what the doctors call "T & A," for tonsillectomy and adenoidectomy. A cassette tape of a snoring child made by the parents should be satisfactory evidence of the condition, along with the observation by the doctor of the enlargement. (At one treatment center the cassette is played into a computer, which can tell from the snores how much airway obstruction exists.)

Grundfast, who admits he was a skeptic himself as recently as three years ago, is now convinced that open-mouthed daytime breathing of the child with enlarged adenoids can cause significant facial abnormalities.

Obstructed breathing at night, evidenced by the snoring, also can be associated with bedwetting and possibly with somewhat limited growth. (The growth hormone is disseminated at night, notes Grundfast, suggesting a possibility, as yet unconfirmed, that oxygen deprivation could be responsible.)

Other symptoms of obstructed breathing can be restless sleeping (tossing and turning), daytime sleepiness and poor school performance.

Among surgical updates:

* Adenoids only can be removed (without an overnight hospital stay) when they block nasal breathing, when there is abnormal speech or recurring ear and sinus infections and chronic runny nose.

* Tonsils only (requiring a one-night stay in most places and not even that in others) may be removed when there has been frequent tonsillitis or a tendency to collect debris causing oral-hygiene problems like bad breath.

Dr. David Fairbanks of the George Washington University Medical Center says that by the age of 3 years, most of the immunological advantages offered by tonsils and adenoids have run their course. After that, they should be removed when symptoms warrant.

In any case, says Grundfast, the operation should not be discounted automatically on the grounds that "it is not done anymore."