Part of the adventure in a Contemporary Music Forum concert is the chance to learn something new. Last night, for example, listeners at the Corcoran Gallery found out about "Diatomaceous Earth," a soil composed of the cell walls of one-celled animals and used as a filler or abrasive. It also proved to be a short, inventive work for bass clarinet and vibraphone by a young composer from New York named David Deason, who may or may not have meant anthing by the title. One performer suggested it was meant to imply "either purification or irritation."

Quite clear in its meaning was an evocative work by Washington composer Frances McKay entitled "Elegy in the Form of a Dream." This work, like the Forum concerts themselves, points up an increasing interest and success in reaching out to the listener. Both musically and verbally, Forum musicians seem to be striving to improve communication without compromising their high standards or commitment.

Joining the Forum for the first time was cellist Evelyn Elsing, who gave a compelling performance of Davidovsky's elegant "Synchronisms No. 3." The program concluded with Robert Hall Lewis' highly effective and accessible "Toccata for Violin and Percussion" which, like the other works on the program, received a splendid performance.