San Francisco — In our present electronic age, when words are more often heard than seen in print, it may be necessary to take a methodical approach to vocabulary building. As students begin the exciting but arduous task of building more extensive and useful vocabularies, they should be reminded that great writers - Jack London and Robert Louis Stevenson, for example - did not use ''big'' words merely to show off. They used them for precision.
There are other ways to help children increase their vocabularies. One, a recommended vocabulary program, is based on an elaborate flashcard system.
When the student encounters an unfamiliar word in his reading, he writes it down on the blank side of an index card.
Turning the card over to its lined side, the student then copies the sentence in which the vocabulary word appeared, circling also the word itself. (If the sentence is overly long, this may be indicated with the three-dotted ellipsis; just enough of the sentence is written to give a sense of the word's meaning.)
For the second entry, the student copies the dictionary definition that is most appropriate, remembering that a single word may have a number of meanings.
The third entry - and the only one written in pencil - is a sentence, written by the student, used to reflect the meaning of the word as it was used by the author. If students are encouraged to write complex sentences, then one of the clauses is likely to convey or enhance the meaning of the word. Later, when read by parent or teacher, the student may decide to erase his own sentence and try again. I still remember from my early teaching days a student of mine who impulsively wrote the following sentence to the word, ''mute'': ''My dog is a mute.''
If the student makes four or five vocabulary cards a day, and then studies and reviews the growing collection of words, and then uses them in speaking and writing, it should be possible to make a vocabulary increase of more than 1,000 words a year. Looking at long-term goals, or even short-term goals, this could be considerable.