ONE of the more interesting wrinkles of the current season can be found in the return of ''Fame'' for a third year. The series had been canceled by NBC because of disappointing ratings. That normally spells death on the television circuit. But ''Fame'' was then picked up by a consortium headed by M-G-M Television, to be distributed in syndication to individual stations, some of which, ironically, may be affiliates of NBC. In the New York area, the weekly show can be seen on WNEW-TV, Channel 5, beginning Sunday at 5 P.M.
       
On its return, the series has lost some of its regular characters, most notably Julie, the attractive cellist who, we are told, has run off to marry a lifeguard jock in Texas. Joining the cast as new first-year students at New York's High School of Performing Arts are Holly (Cynthia Gibb), a drama major, and Christopher (Billy Hufsey), a dancer who just might pose a competitive threat to the cocky Leroy (Gene Anthony Ray).
Complicating matters further is the appearance of a new assistant principal (Ken Swafford), who is a traditional academic, going strictly by the book and not impressed with the ''artsy-craftsy'' ways of this particular school. Otherwise, everything remains pretty much the same, right down to the ''spontaneous'' outbursts of dancing and singing that obviously required hours of rehearsal.
                   
This first episode, which will be concluded on the following Sunday, revolves around the sensitive young musician-composer Bruno (Lee Curreri), whose widower father dies. Bruno will be forced to leave school if no way is found to finance his education. The sympathetic teachers, especially the elderly and wise Mr. Shorofsky (Albert Hague), are rallying to his side.
                   
Written by William Blinn, ''Fame'' remains an uncommonly appealing show, offering something a bit different from the usual sitcom or action- adventure romp. Each week, it turns into a kind of miniature musical, with roots going back to ''42d Street'' and the like. It would be nice to see it succeed solidly in this country, especially because it has done so well in European markets, a factor that undoubtedly was not overlooked by the syndicators.