A 19th-century opera gala restaged on TV

It may have seemed like a charming idea to restage a 19th-century opera gala for modern stereo simulcast televsion. And Rossini at Versailles (Dec. 27, PBS, check local listings) has some splendid singing to offer, particularly from Marilyn Horne and Montserrat Caball'e. It is filmed in the Royal Opera House and Chapel of the legendary royal palace outside Paris. For musical continuity, maestro Claudio Abbado is in the pit with the Chamber Orchestra of Europe -- a talented gathering of the finest young musicians of Western Europe.

The two above-mentioned ladies are in excellent voice. With ease, Miss Horne tosses off an aria from ``Semiramide,'' a Spanish song, and various duets and ensembles. Miss Caball'e's legendary pianissimos are heard to great advantage, and she and Miss Horne make a rare duet appearance in a selection from ``Tancredi.'' Other outstanding moments include Francisco Araiza's ``Cujus animam'' from the ``Stabat Mater,'' Ruggero Raimondi's run-through of a catalog of accents during an aria from ``Il Viaggio a R eims,'' and the first act finale from Rossini's ``L'Italiana in Algeri,'' which concludes the program.

The success of the vocal contributions is considerably aided by Mr. Abbado, who is one of the finest opera conductors of the day. He knows how to keep a musical line alive while allowing his singers room to really make something of that line -- a vanishing conductorly art in this age of metronomic rigidity.

Had the program remained primarily a concert in period costume, it might have been enchanting. But a weak scenario is thrown in, involving Rossini (played by Paul Brooke), who is first seen chewing on a piece of chicken and later observed beaming at Miss Horne, gazing into some imaginary distance during his devotional music, etc. The scenario lacks charm and gives a rather plastic look to what is basically a sing feast for all to enjoy.