Morton Subotnick's quite outrageous "Liquid Strata," which was played by pianist Alan Marks in the University of Maryland's piano festival last night, requires a word of explanation.

Subotnick's works, which are heard with fair frequency here, normally combine standard instruments with electronic ones, like synthesizers--with a result that is a bit like space-age chamber music. "Liquid Strata," a three-movement work of about 15 minutes, is for two instruments all right, but the explanation on the program that it is written "for piano and ghost electronic score" raises more questions than it answers.

Marks, who was the first-place winner of the Maryland piano competition 10 years ago, tried to explain the score further before he launched into the music. "It is actually two separate compositions," he related. "One is an actual noted piano score," which he pointed to on the rack of the piano. "Then," he continued, pointing to the speakers on either side of the stage, "there is a composition for tape, connected electronically with the piano" in which the sounds of the piano are programmed to sound like "wa-wa" or whatever.

In other words, it's another form of the amplified piano that John Cage has raised to heights of ear-splitting cacophony.

"Liquid Strata" has to do, in general, with spatial effects in sound, accompanied by such eccentricities as the pianist reading excerpts from Sir Isaac Newton.

As such works go, it was more agreeable than most. The central section showed a real sensitivity for delicate timbres. And, for once, there was a sense of forward momentum in this sonic maze--a sense of direction, with even some harmonic underpinnings in places.

Marks appeased the audience at the Tawes Theater with an otherwise unconfrontational program. It was a gentle one of Haydn, Schubert and Chopin--all of it played with light inflection and lovely tone.

If the Steinway on which he played sounded tonally shaky at times, that may have come as the result of the assault it sustained in the afternoon from a performance in this year's semifinals of the piano contest. A little-known, 30-year-old pianist named Howard Lubin played an overwhelming performance of Liszt's herculean B-minor sonata.