When they're in doubt at public television -- and they usually have good reason to be in doubt--they say, "Let's do a Eubie Blake special." The late Mr. Blake did not lack for tributes in his golden years, even though his output as a composer pales in comparison to that of the Gershwins, or Irving Berlin, or Jerome Kern, or any of a number of other American composers public TV has not found it chic to celebrate.

"Eubie Blake, A Century of Music," taped at the Kennedy Center shortly before the composer's death and airing at 9 tonight on Channels 26 and 32, is a great quaint bore, at least until, in the second half of the 90-minute special, such performers as Joe Williams, Rosemary Clooney and Cab Calloway take over. As the Blake numbers trot by, their lack of distinction becomes almost embarrassing. Except for gems like "Memories of You" and "I'm Just Wild About Harry," there isn't a lot in the repertoire on which to feast.

The evening--poorly directed by Dick Feldman and awkwardly shot by the assembled camera crew--would surely have been perked up and redeemed if Blake himself had performed, but, having just turned 100, he apparently was not up to that. Most of those who sing his songs on the special--Lola Falana, Patti LaBelle, Anita Morris and others--do so in mediocre style. The production was staged with far too much extraneous, distracting movement by a troupe of annoyingly busy dancers who are often encumbered with decorative flats they must haul about and with which they play silly games of peekaboo.

Near the end of the program, a taped insert featuring Stevie Wonder (not present at the Kennedy Center) singing "Goodnight, Angeline," accompanied by an old Blake piano roll of the song, is an elegant moment, but the prevailing motif on this special is cute desperation; it's just a dreadful, debilitated drag. And it has built into it three interruptions for pledge breaks by PBS stations, which, during their most recent pledge weeks, promised us--didn't they?--they wouldn't be doing that again for months. Public television remains its own worst enemy, and no great friend of viewerkind, either.