There is a big difference between "electric" and "electronic," especially as both words apply to rock music.

"Electric" generally refers to the instruments - guitars, bass, even drums - that are extensively amplified in large arenas. "Electronic" means the effects produced by a non instrument now firmly entrenched in the makeup of most rock'n'roll bands: the synthesizer.

Emerson, Lake and Palmer, appearing at the University of Maryland's Cole Field-house Saturday night, will not back for synthesizers. Keith Emerson was one of the first to employ the Moog and, though recently his reputation has suffered a bit through self-indulgence, he remains one of the primary users of rock electronics.

The acceptance of the synthesizer into rock's mainstream has changed the sound of the music more than any other single influence. The irony for ELP is that originally they were hailed as the first major group to incorporate classical music into their sound, dating back to Emerson's symphonic work while leader of The Nice.

The fact is that ELP's use of classical configurations and titles (like Emerson's "Piano Concerto No. 1") does not make it "classical" any more than Chicago's use of horns makes that group a jazz band. All three members of ELP have had at least some classical training, but the influence is more implied than performed. Their electronic prowess, however, is much easier to hear.

Emerson was wowing crowds in 1971 with his Moogs and ARPs when only Yes (then just two albums old) and the Moody Blues were using them with any sucess. Mike Pinder's mastery of the synthesizer allowed the Moodies to effect their string backgrounds without using a full orchestra the way they did on "Days of Future Passed." (ELP just fired its road orchestra for financial reasons. Emerson now uses his arsenal of electronic gadgetry to produce nearly the same sound.)

There are several types of synthesizers: pre-set, string ensemble, self-contained, mini-Moog and a percussion device. All process sounds electronically in a desired range, and the possibilities for reproduction are infinite.

Saturday, in addition to the usual variety of gizmos, Emerson should use his new toy, the Yamaha GX-1, a $50,000 "Dream Machine" first used by Stevie Wonder but improved by Emerson and his electrician (whom Emerson needs the way Clapton needs a guitar; many purists point to this as evidence that music will be subjugated to electrical engineers, but the machines seem here to stay, purists or no).

Musicians can take some solace in the knowledge that a good synthesizer player usually is an excellent keyboardist by necessity. The best at handling electronics have proven skills at piano: Rick Wakeman, Gary Wright and Edgar Froese of Tangerine Dream, to name just a few.

Also, the machines have altered musical directions and improved the overall sound of many bands. George Duke, Ronnie Laws and - to an extent - Chick Corea have gone from talented but largely neglected jazz sideman to mass-audience attractions by adopting synthesizers. Fusion music is a direct result of the synthesizer.

Walter Carlos has made a career of programming classics for Moog, and Heart's latest single, "Heartless," is transformed into a soaring grabber when the ARP sneaks in under the Wilson Sisters' vocal harmony, pulsates at their exact pitch for an instant, then dips into the lower register like an electronic roller-coaster.

Saturday night should be a clinic in the use of electronics. Though Emerson, Lake and Palmer were not the first to use the synthesizer, they were pioneers in expanding its limits. Now the question is whether the electronics will outgrow the bands that made them famous.