Mickey Rooney in a touching special - and a grim documentary

Call me Scrooge, if you will, but this is the season in which, for me, ''the vast wasteland'' some people call TV turns into a vast sea of molasses. Everybody from Charlie Brown to Charlie's Angels dusts off ye olde Christmas tale and retells it for an audience up to its ears in peppermint sticks and sugarplums, whatever they are.

This year is no exception - coming up in the next few days are ''Santa Claus Is Coming to Town'' (ABC, Saturday), ''A Christmas Carol at Ford's Theatre'' (PBS, Saturday), ''Bob Hope's Annual Christmas Bagful of Stars - etc.'' (Sunday, NBC), ''Rudolph and Frosty'' (ABC, Sunday), and many more such shows on local and network stations, too numerous and too similar to list individually.

But I must admit that one of the Christmas shows I will be watching (again, that is, since I have already done my previewing duties) will be my absolute favorite of the year - a feisty, soapy, sentimental, inspiring GE Theater show titled ''Bill'' (CBS, 9-11 p.m., check local listings).

Written with skill and economy by Corey Blechman, directed with joyful innocence by Anthony Page, ''Bill'' is a fact-based drama starring Mickey Rooney as a retarded man who finds friendship and love when a young filmmaker, played by Dennis Quaid, comes into his lonely life.

Says the filmmaker, played with breathtaking believability by Quaid: ''I don't want to lose the ability to care, to be concerned about another human being,'' when he is finally forced to assume responsibility for the man to prevent him from being institutionalized at the same place where he had spent the first 44 years of his life.

Mickey Rooney portrays the retarded man with utter restraint - there is not one telltale sign of the wild and comic Mickey in the character, only the caring , insightful signs of the man who must exist behind the comedian's mask. It could be an Emmy-winning performance, and one hopes when the awards are handed out that Bill Sackter, the real man upon whom the story is based, will be there as well. 'Rain of Terror'

Every now and then a television documentary manages to pinpoint, with its uniquely personalized style, important events that have been going on in the world, perhaps already noted by other media but not really given the attention required. ''ABC News Closeup: Rain of Terror'' (ABC, Monday, Dec. 21, 8-9 p.m.) is such a documentary.

Be forewarned there are horrifying pictures which may disconcert you. But in a thought-provoking and incisive text, it tells an astounding tale of alleged Soviet use of poison gas against Yemen, Afghanistan, Vietnam, and Hmong tribesmen in Laos.

This ABC Closeup, directed by Pat Cook, with correspondent Bill Redeker using a script done by him and Steve Singer (who also produced the documentary), attacks not only the Soviets but also charges that United States bureacratic bumbling has only halfheartedly investigated the claims and tested the samples of mycotoxins laced with polyethyleneglycol which survivors have brought back from Southeast Asia and Afghanistan.

While officially the scientific world throws doubts on the credibility of the testing methods, the show says thousands of Asians continue to die of something they call ''the yellow death.'' ABC Closeup, under initiative of Pamela Hill and Robert Richter, takes a new initiative, even to the extent of hiring its own scientists to make tests. Other media have also reported this phenomenon, and this newspaper will carry an article on the subject the day the ABC special airs (Dec. 21).

''Rain of Terror'' is a shocker, but it has important things to say. Bill Redeker says, ''This is an issue which affects the basic human right to live free from terror and intimidation. Lives are now at stake in Southeast Asia - there may be more elsewhere in the future.'' Worth noting

SATURDAY

PBS: A Christmas Carol at Ford's Theatre (8-10 p.m.)

SUNDAY

PBS: In Performance at the White House: Beverly Sills and her Protegees (10- 11 p.m.)

MONDAY

NBC: Little House on the Prairie (8-9 p.m.)

All the Way Home (9-11 p.m.). Live revival of Tad Mosel's classic play, with Sally Field and William Hurt

PBS: Great Performances (8-10 p.m.). Repeat of the San Francisco Ballet's ''The Tempest''

TUESDAY

ABC: John Denver and the Muppets (8-9 p.m.)

PBS: Odyssey (9-9:30 p.m.). ''Some Women of Marrakech''

WEDNESDAY

PBS: Christmas with Pavarotti (8-9 p.m.)

Giulini Concerts - L. A. Philharmonic (9-10 p.m.)

(Check all PBS listings since local stations often vary airing times)