WORTH NOTING ON TV

THURSDAY `Yo-Yo Ma: A Month at Tanglewood': (A&E cable, 9-11 p.m.): You dog the footsteps of the world-renowned cellist as he moves from master class to rehearsal to performance at the Boston Symphony's summer home in this revealing peek at the world of music. The second half traces a Nali Gruber cello concerto from creation to its premi`ere by Ma. SATURDAY Comic Relief '90 (HBO, 8 p.m.-1 a.m.): Billy Crystal, Whoopi, Goldberg, and Robin Williams are hosts to an awesome lineup of talent in this year's version of the live marathon show benefiting the poor and homeless. (HBO will ``open'' its signal so basic cable homes can see the program).

SUNDAY `Platoon' (ABC, 9-11:30 p.m.): Network premi`ere of the multi-Oscar-winning 1986 film about a young soldier's life in the Vietnam War. Its harrowing realism - both physical and emotional - shocked many audiences into a latter-day awareness of what that struggle was really like.

WEDNESDAY `Sing! Sesame Street' (PBS, 8-9 p.m.): Everyone from Barbara Bush to Candice Bergen appears in this salute to the man behind the music of the classic children's show - the late composer Joe Raposo - who's joyous ``Sing!'' became a much-recorded musical point of view. Lots of old clips and new acts - muppet and human.

Please check local listings for all programs, especially on PBS.