Science teacher Pat Hagan paced her Gaithersburg classroom at Montgomery Village Intermediate School, firing off questions about heat transfer to 29 eighth graders, rapping a desktop here and there to get a young mind in gear. In her hand was a remote control device. By the lab table up front was a large-screen TV, with an electronic box resembling a VCR perched beneath it.

Hagan punched keys on the remote control and a still photo of an ice cream cone that was starting to melt appeared on the TV screen. "Tell me why this happens," Hagan said to the class, which was meeting before school let out for the summer.

"Right," Hagan said to a volunteer with the correct answer, "you have radiant heat coming down and starting the ice cream to melt." Later in the class, she punched more buttons and a brief film demonstrating different kinds of heat started to roll.

What Hagan and her students were using is a laser videodisc, yet another example of new technology filtering down to alter daily life in America. Already established in industrial and military training -- Ford Motor Co., for instance, has used discs to train mechanics -- it is now starting to show up in ordinary classrooms.

All of Montgomery County's high schools and many of its lower schools now have disc players. Several other school systems around the Washington area have also bought into the technology or served as test sites for it. Nationwide, an estimated 20,000 videodisc players are in public and private schools.

Many teachers swear by this addition to the "electronic classroom." The technology appeals in a positive, stimulating way to the learning orientation of the MTV generation, they say. "These kids are visually oriented," said Carol Muscara, a computer instruction official in the Montgomery school system. "We've trained them that way. They've been watching Sesame Street since they were three years old."

In the right teacher's hands, fans of the technology contend, discs encourage active participation by students. They can be used intermittently during a class to spice up a discussion, unlike a film that runs 20 minutes and evokes a largely passive response. Discs allow teachers to customize a lecture or discussion, using the remote control to call up only specific portions of the disc to make the points they want to make.

But the technology is not for everyone. Cost of the players start at about $400, while the individual discs run about $500, prices that may not appeal to schools with low budgets and competing needs. Moreover, there is no guarantee that teachers will use them to anywhere near their full potential. Like the personal computer, theoretically a teaching tool of immense power, discs could remain on the sidelines of mainstream education.

In addition, some parents and teachers object to the approach itself, arguing that the video medium will deliver another blow to American children's faltering ability to read. But for now, this camp seems very much to be the minority. "It's a skyrocketing area," said Lyle Hamilton, disc advocate and manager of broadcast for the National Education Association, which represents teachers.

Twelve inches across, the discs look like overblown versions of the compact discs of home stereo systems and harness the same laser-based optical technology. In general, they yield sharper pictures than videocassette tapes.

In the early '80s, the entertainment industry pitched them to consumers, releasing films on disc only to see the medium lose out to cassettes, which could record material as well as play it. But educators like two things that disc players can do that videocassette recorders cannot: freeze a frame in a film clip crisply and indefinitely and, in a maximum of 10 seconds, search out and display any frame or clip on the disc.

More than 300 educational discs are now on the market. Some are simple re-releases of old films. Others, like the one Hagan used, function as libraries of visual information aimed at complementing textbooks and lectures. The discs are filled with film clips, still images, diagrams, animations, maps, charts and illustrations -- up to 54,000 still images per side. With an index in hand, a teacher can plan a specific sequence of illustrations for a specific class.

A few large Japanese companies control the disc player market. Putting material on the discs, however, is the preserve of a diverse collection of U.S. companies, some of them small and shaky, others big -- National Geographic Society and ABC News, for example. The disc "publishing" industry has sprung up largely independent of textbook companies. But now the two media are starting to be coordinated, as disc companies put out products geared for use with specific books.

Debbie Dasgupta, one of Hagan's students, said she saw the video player as "a backup for the book." It made "a lasting impression on the mind, so you can remember things a lot longer," she said. "So it's a really fun way to learn." Student Adriana Marquez was also upbeat: "It interests people more than just drawing on a blackboard."

Saira Kahn, another of Hagan's students, was skeptical, however. "It's just there. It's something you look at," she said. " ... It's nice to have but it's not something that schools should go out of their way to buy."

Responses like Kahn's haven't been enough to stop school systems from giving the technology a lift. Texas has spent $5 million to develop discs for science instruction. But overall, discs are no shoo-in. "For something new to move in the front door, something old has to move out the back door," noted William Clark, president of Optical Data Corp. of Warren, N.J., a major producer of educational discs.

Teachers, meanwhile, continue to experiment on how best to employ them. Hagan generally has used her players manually, creating a sometimes awkward pause as she punches into her remote control device frame index numbers that bring up specific images. At times, she has used it connected to a personal computer. That way, a lesson can be mapped out in advance and striking a single key on the computer moves the player to the next frame.

Here and there students are using discs as part of complex "multimedia" systems. Sitting at computers, they merge video footage, sounds, still images, text that they write themselves, charts and computer data to produce the electronic equivalent of a term paper -- a presentation on the campaign of Rep. Richard Gephardt (D-Mo.), for instance, drawing on material from an ABC News disc about the 1988 presidential race.

Some educational specialists, however, warn against going in that direction. Disc players are most likely to gain wide use if they are simple and inexpensive to use. Schools don't always have the funds for computers, it is pointed out, and teachers may feel as intimidated as the students in using them. By fits and starts, the technology continues to advance, though most schools remain without them. But, as Frank B. Withrow, team leader for the technology applications group at the U.S. Department of Education, noted: "It's more than a fad."