While still limping into classrooms after more than a decade, computers for teaching have burst into homes.

A total of 18 million units, marketed as educational electronic games or computer learning aids, were sold to consumers during 1979 and 1980, according to industry estimates. Retailers say sales have continued to grow this year as children are drawn to the computers' disembodied voices, quick answers and flashing lights, and parents buy them in hopes of boosting the youngsters' academic skills.

Although the small computers' fascination is clear, their value for learning is uncertain. So far, virtually no systematic research has been completed to assess the claims of their makers that the machines raise achievement by holding children's interest so well that youngsters drill and practice more than they normally would.

"I think these devices can be useful," said Charles Tidball, a computer education expert at George Washington University, "but it depends on what support the child is getting outside. The computer is better than nothing, and I'd much rather see parents buy one with educational objectives than just a game. But to get a great deal from it, I think a parent or some other adult has to take the time to be involved. There are no major shortcuts. You should resist the hard sell."

"We don't claim to replace the teacher or anything that should go on between parent and child," said Ralph Oliva, director of computer learning aids for Texas Instruments, the largest maker of the devices. "We see them as enrichment that provides drill and practice along with fun . . . . This is an alternative to the action games that adds productivity to leisure time. It's electronic and fun and has educational value."

Despite inflation, prices for the computer learning aids, widely advertised for Christmas, have dipped this year.They range from under $10 for simple models that look like hand-held calculators dressed as plastic owls, to about $130 for desk-top computers with music and TV-like screens. Their target audiences range from 4-year-olds for whom one company offers a "computer-programmed friend," to students in junior high, who are challenged with spelling quizzes and math games.

"Some of the learning aids are so popular, I can't keep them in stock," said David Dunnell, a salesman at Chafitz Electronics in Rockville. "They're sort of between television and a book . . . . Of course, one thing that sells them is that parents are concerned about the schools."

All of the machines are based on micro-computer chips, which reduce elaborate electronic circuitry that once occupied large rooms to small silicon discs. The first one, Texas Instruments' Little Professor, came on the market just five years ago. It resembles a hand-held calculator with big keys and a bright plastic face, but instead of giving answers, Little Professor gives problems and then corrects answers, functioning as an electronic flash card for mathematics practice and drill.

Texas Instruments later added Speak & Spell, Speak & Math, and Speak & Read -- three machines that imitate human speech, using a synthesizer embedded in a silicon chip. With the same friendly baritone, they all ask their questions and then calmly prod, correct, or reward, depending on the answers received.

In the "Electronic Learning Machine" by Coleco, green lights flash and a happy tune plays when the right answer is given. There are red lights and unphappy chords if the answer is wrong.

Mattel's "Children's Discovery System" includes a keyboard, musical sound effects, and animation on a viewing screen that tries to teach not only spelling and vocabulary, but also music and art.

"The whole idea is to have a multisensory environment that interacts with the child," said Dunnell. "The kids get more involved than when they just have a book that they have to look at or a teacher who stands at the front of the room."

Kenneth Komoski, executive director of the Education Products Information Exchange (EPIE), an independent consumer-oriented group, is more cautious.

"It's true that the kids were enthralled with these machines," said Komoski, who wrote a report for the Ford Foundation on the computer learning aids. "But we found that the thrall wore off pretty quickly."

"They're useful for practice of math operations or spelling that children already know," Komoski continued. "But we identified very little new learning taking place . . . .There are lots of bells and whistles, but inside they're not much more than drill and flashcards, maybe electronic workbooks. You have to wonder whether you want spend the money for what you get."

Although the companies involved do not release sales figures for particular products, "Leisure Time Electronics," a trade magazine, says that in 1980 about 10.7 million computer learning aids and games were sold to consumers, including the machines and their add-on cartridges and modules, with a retail value of$174 million. In 1979, about 7.5 million units were sold valued at$96 million.

By contrast, despite extensive publicity, the use of computers for teaching in schools has remained small, according to researchers at the National Institute of Education.

"Some of them have been effective," said Patricia Butler, an NIE associate, "but because of the costs involved, they haven't been accepted."

Costs are now coming down with the introduction of home computers priced at about $400 that plug into television sets, and Butler said that with those cheaper machines available, the schools are beginning to use computers more. But she said that the much-predicted "computer revolution" in schools is "still far from happening."

Most of the sophisticated home computers and video games now available in the stores, such as Atari, Texas Instruments, and Mattel's Intellivision, also have cartridges with educational programs. So far, the sales of education cartridges lag far behind those of sports and space games, although the manufacturers report that the education market is growing.

The upsurge in the smaller, hand-held computer learning aids over the past three years is part of the boom in electronic games. Last year, sales of the sports and "action" games were about five times greater than the education aids, according to Thomas Kully, a toy industry analyst at the brokerage and investment firm of William Blair & Co. in Chicago.

But Kully said that the game field became overcrowded, and a glut of unsold merchandise has forced sharp cuts in price. The education aids, which use much of the same technology, have continued to have "strong growth," Kully said.

"The sports games have fallen off a lot from their heyday two years ago," said Michael Katz, a vice president at Coleco. "The hottest things right now are the arcade-type games. But I think the education games are for the long haul and they keep on growing."

Even though two major firms entered the computer education market this year, Kully said, Texas Instruments "dominates" the field, probably because of the appeal of its speech simulator.

In Speak & Spell, the voice starts by saying "Hi," and then patiently teaches the spelling of 150 words. There also are secret codes and "mystery words," and five cartridges are available with 150 more words apiece

At one point the voice says, "Try ocean," and as a child pecks on an alphabet keyboard, the letters flash on a screen, o-c-e-a-n. The voice intones each one after it appears. When the child is done, he presses the key marked, "ENTER," and receives an encouraging: "You're right."

"Now spell warm," the voice continues. "W-u-r-m," the child attempts. "Wrong, try again," the voice declares, repeating, "warm."

"W-e-r-m" is the second attempt.

"That is incorrect," says the voice, still pleasant. "The correct spelling of warm is w-a-r-m," and the correctly spelled word flashes on the screen. "Now spell sure" -- and the lesson continues.

Tidball, of George Washington University, said that, by itself, the simulated speech "doesn't make the computers any better as an education device. It doesn't make them better than an interested and available human being that's much more creative and responsive than any computer."