Oleg and Ludmila Protopopov, the four-time world-champion skaters, made their belated Washington debut last night. Her bout with the flu had kept the pair from appearing with the ice Capades at the Capital Centre last week, but they are scheduled to be on all of this final week's programs.

It was apparent that not only the Protopopovs, but quite a few other skaters in this 40th-anniversary edition of the Capades have had ballet training. The two techniques, skating and ballet, have much more in common than disco dancing and skating or high-wire acrobatics and ballet, which others have tried to join. Their emphasis on long sweeping lines and fluid execution makes them naturals to be tried together. Balletic turn-out of the hips gives the skater's legwork greater facility and visibility, and the pulled-up, gently arched balletic spine lends unending turns on ice a seamless ease.

Such balletic ice dancing isn't at all new, as 1940s movies with Sonja Henie, Vera Hruba Ralston and Belita will attest. But the Protopopovs have applied ballet movements to their ice work with extraordinary consistency. h

The pair's elegantily articulated port de bras -- the carriage of the hands, arms and shoulders -- and their heads held high with ease are hallmarks of their Russian dance training. There is no sign of strain in the back as they turn or in the legs as the glide in arabesque. Even skating's most anti-balletic feature -- the protruding rear that serves to absorb shock in acceleration steps or is used as leverage in changing directions -- is almost invisible in theProtopopovs' proud line.

Technically, they are artists. What they perform could be serious too, even in the context of an ice revue. After all, Anna Pavlova gave "The Sleeping Beauty" its U.S. debut on a circus bill between elephants and tumbling acts. The music the Protopopovs used is by Beethoven and Saint-Saens. Their ice pas de deux, though, are closer to the sentimental show-biz routines of some of their current colleagues and to the mood and display duets of the Bolshoi Ballet than to such substantial choreography as that of "Sleeping Beauty."