Gilbert and Sullivan's most operatic operetta. "The Yeoman of the Guard." had somewhat less success upon its opening in 1888 than even its immediate predecessor, the ont especially memorable "Ruddigore." But in retrospect "Yeoman" is possibly the strongest, both musically and dramatically, of all the G&S repertoire.

Now, thanks to the British Broadcasting Company, it has been brought to film - to be broadcast at 9 tonight on Channel 26 and again Saturday on Channel 22, this week's offering on Opera Theater.

The BBC touch loses none of its proven magic in this production - the kind of Gilbert and Sullivan you dream about and rarely, even with the D'Ogyly Carte Company itself, can see on stage or on screen.

Gone are such all-too-common irritations as misplaced sound equipment distorting critical Gilbertian rhymes and conundrums. Or underrehearsed pickup orchestras out of synch with the singers. Virtually every syllable, sung or uttered, is distinct. The New Philharmonia Orchestra conducted by David Lloyd-Jones is neither "pickup" nor underrehersed, and it has to pay off.

"Yeoman" is presented as opera and comes across as opera, this classic story of the tragic jester and his ill-fated love, all conducted on the green of Tower of London.

Film techniques accent the drama without impugning the integrity of this gem of a light opera, which, by the by,includes the one song written wholly - words and music - by W.S. Gilbert and that one no less than the show-stopper "I Have a Song to Sing, O!"

A strong cast including Valerie Masterson (out of D'Oyly Carte), David Hillman, Derek Hammond-Stroud as Jack Point, the jester, and Dennis Wicks as Wilfred Shadbolt along with the splendid Ambrosian Opera Chorus, make this far and away the finest film version of any Gilbert and Sullivan opera. an at 5 p.m. and ended at around 11:20, several hundred patrons sat down