If actors could sue writers and directors for letting them down, LeVar Burton and Paul Sorvino might have a case over "Dummy," the highly disorganized but potentially fascinating CBS movie Sunday night at 9 on Channel 9.

Ernest Tidyman adapted the screenplay from his own book, based on the case of a young black Chicago man who could not speak, hear, read or write but was charged with the murder of a prostitute in 1965. The film tells how the young man's attorney, who is deaf but can speak, tries to keep him from being ground to dust by a bureaucratic judicial system with no special dispensations for the chronically or uniquely handicapped.

LeVar Burton, who exploded onto the television screen in "Roots," plays Donald Land, the accused youth, and obviously must do all his acting with facial and physical resources. These are formidable; Burton flashes the haunted, threatened look that is probably the single most memorable image from "Roots." But he does more than a study in pathos. His performance is a definitive portrait of isolation and alienation, conditions that are only made worse when the state orders him to a mental institution after ruling he is "incompetent" to stand trial.

As the lawyer, Paul Sorvino also does an impressive job with a difficult character, although Sorvino's attempt to emulate the speech patterns of a deaf person who has been taught to speak occasionally just sounds like Dom DeLuise talking normally. It is still a forceful portrayal, however, and the bond formed between the lawyer and his client is emotionally gratifying.

Unfortunately, just as the two characters must battle the system, the two actors must contend with Tidyman's anything but tidy screenplay - a splotchy scrapbook of flashbacks, imcomplete scenes of gaping holes - and the quixotic, ineffectual direction of filmmaker Frank Perry. If any story cries out for a straightforward documentary style, this one does, but watching it is like listening to an endless anecdote being reeled off by a master of free association.

The most annoying of all the ill-advised touches in this production is one of the most inappropriate and undistinguished musical scores ever written for a TV movie-and that's going some. Gil Askeyis slack mock-rock score is a honky-tonky intrusion on the mood of the film and the simple progress of the narrative, which has enough problems as it is . For not only surviving all this botchulism but triumphing over it, Sorvino and, more strikingly, Burton deserve commendation and gratitude.

As is noted at the end of the film, Lang was eventually cleared of the murder of the prostitute but then, six months later, was accused of the murder of yet another prostitute. The movie ends with a freeze frame and the narrator, Sorvino, wondering whatever will become of Lang. In fact, he was convicted of the second murder but the conviction was overturned in 1975 on the grounds that Lang has not been able to participate in his own defense.

The film is dedicated to the idea that there will always be those for whom society must bend its rules and make allowances, but whether Lang makes a perfect symbol for thses special cases we may never know. One hopes the next Donald Lang will have more eloquent defenders than Tidyman and Perry and nobody orchestrating his plight as if it were the latest thing in disco dances.

'Best Place to Be'

The best place to be Sunday and Monday night would have to be any place but NBC, where Ross Hunter's unspeakably slurpy melodrama "The Best Place to Be" will occupy four woozy hours of prime-time TV, starting at 9 each night on Channel 4.

A Ross Hunter movie is always an outfit movie, and so in "Best Place," the tale of a middle-aged widow who goes on tip-toe to the dogs, star Donna Reed has an outfit for every occasion - a funeral outfit, a morning-after-the-funeral outfit, and lots of outfits for receiving nasty phone calls about her teen-age son turning into an alcoholic thief or her daughter smoking pot and joining a hapless rock band called The Pot Boilers. Perhaps they boil it before they smoke it.

What writer Stanford Whitmore (adapting a Helen Van Slyke "novel") and director David Miller have done is to take the old and much-missed Carol Burnett soap opera spoof, "As The Stomach Turns," and played it straight. So when the handsome young doctor knocks at the door and Donna Reed opens it, he all but says, "Hello, I'm the handsome young doctor with whom you will have a passionate but ill-fated affair."

Reed stalks numbly through a hilarious procession of calamities, her hair never mussed, her upper lip unfailingly stiff. Maybe a face lift prevents one from opening one's mouth very wide, because she does appear to be whispering all her lines. Then again one can hardly blame her for being embarrassed by them.

Producer Hunter turned to television when his movies started flopping; he still shows the same kitschy passion for decor and gowns and the same disdain for anything remotely related to human conditions. By twice identifying the New York skyline with the legend "New York City" and the Golden Gate Bridge with "San Francisco," he also lets his audience know just how bright he thinks it is. One clings to the hope that that audience has all but vanished from the face of the earth. CAPTION: Picture, LeVar Burton in "Dummy"