The only point in doing "The Miracle Worker" again was to give Patty Duke Astin a chance on the other side of the food. In the Broadway and film versions of this spendid play about the young, blind and deaf Helen Keller, Astin -- then a child -- did the throwing. Now she plays Keller's resolute teacher, Annie Sullivan, and she gets to do the ducking.

Unfortunately, an altogether satisfactory film version of "The Miracle Worker" already exists, so NBC's new two-hour film, Sunday at 8 p.m. on Channel 4, seems otherwise on the gratultous side. Also working against it is careless casting in some of the smaller roles and the usual flat, hideous,inexpensive lighting that haunts most of these made-for-TV movies.

It should be remembered that "The Miracle Worker" started as a television show -- a live "Playhouse 90" in 1957. To do it now as a film for television is almost to insult its origins. They should have done it on tape in a studio and made it Real TV.

Melissa Gilbert, of "Little House on the Prairie," plays Helen Keller this time, and while she is very, very conscientious in the role, she is physically too big against the petite Astin to make their many struggles and tussles very believable. If they'd been this evenly matched, Annie Sullivan probably would have been knocked unconscious the first day she arrived at the Keller home to take over as governess.

And Astin, though also working hard as Sullivan, has nothing like the authority and the mystery that Anne Bancroft brought to the part on stage and film. Occasionally the squinting Austin brings to ming Gilda Radner as Emily Litella, which doesn't help.

All this said, William Gibson's play about a remarkable teacher and her incredible pupil remains, even when not perfectly done, a nearly perfect joy, one of the most assuredly affirmative dramatic works to come out of the optimistic '50s. Children who have never seen it should be fascinated, and no one will be cheated. But a showing of Arthur Penn's 1962 movie version would serve the same purpose and also serve the author much better.