WORTH NOTING ON TV

* SATURDAY

NBA All-Star Youth Celebration (Nickelodeon, NBC, TNT, 12 noon-1 p.m. EST): NBA players Sean Elliot, Grant Hill, Joe Smith, and Jerry Stackhouse join 20,000 students from the San Antonio region to celebrate academic achievements and encourage children to stay in school.

* SUNDAY

NBA All-Star Game (NBC, 6-9 p.m. EST): The NBA's favorite and best players convene at the Alamodome in San Antonio for the 46th-annual matchup.

Lois & Clark: the New Adventures of Superman (ABC, 8-9 p.m.): The big moment of this two-year-old series is here: the wedding between Clark Kent (Dean Cain) and Lois Lane (Teri Hatcher). As usual in TV weddings, however, numerous obstacles stand in the way. Will Superman save the day?

The Thorn Birds: the Missing Years (CBS, 9-11 p.m.):

The 1983 epic ''The Thorn Birds,'' the second-highest-rated miniseries in TV history, swept from 1920 to 1962 and chronicled a story of forbidden love between Father Ralph and Meggie. This ''midquel'' returns to 1943, covering a period the original miniseries skipped. Filmed on location in Queensland, Australia, ''The Missing Years'' portrays Father Ralph returning to Drogheda - where Meggie's estranged husband is trying to make amends. Richard Chamberlain reprises his role as Father Ralph; the part of Meggie is played this time by Amanda Donohoe.

The miniseries concludes Tuesday in the same time slot.

* MONDAY

Last of the Czars (Discovery, 10-11 p.m.): The rich history of Russia's final Romanov emperor, Nicholas II, and his czarina, Alexandra, comes to life in this documentary, which continues the next two nights. The program includes updates on the 1991 discovery of the Romanovs' burial site. They were executed in 1918.

The Journey of the African-American Athlete (HBO, 10-11 p.m.): This documentary, timed to Black History Month, traces blacks' challenges and triumphs in sports. Part 1 spans 1875-1950; Part 2, airing Feb. 19, covers 1950-present.

Please check local listings for these programs.