Among the questions raised in "My Body, My Child," the two-hour drama on Channel 7 tonight at 9, the thorniest may well be: What on earth is Vanessa Redgrave doing in this muddle?

Redgrave plays a middle-aged housewife from Middle America, who thinks she is pregnant, although none of her doctors does. Instead, they prescribe pills for her depression, subject her to a barrage of X-rays, feed her with antibiotics, amphetamines, hormones and tranquilizers, until it is discovered that she really is pregnant and the fetus may be permanently damaged.

The dawdling and banal script calls for the actress to flatten out her flamboyance and range, not to mention her British accent, and incarnate a morose version of the suburban everywoman. As Leenie Cabrezi, elementary schoolteacher and fireman's wife, Redgrave's distinctive talents aren't wasted as much they are simply ignored.

Redgrave usually brings an aura of controversy with her, wherever she goes these days, and maybe that is what the producers of this somber show were after when they hired her. "My Body, My Child" certainly yearns to be desperately urgent. It cites a worrisome number of babies born today with a birth defect and explains that in a fair percentage of those cases, the defect is not due to genetic malfunction, but to outside causes--the reckless use of pills, medicine and X-rays. The script, however, never rises above the level of a cautionary tract. While there is some social purpose in alerting pregnant women to the dangers of drugs, there is, in this instance, not a great deal of drama.

Redgrave's character spends the first hour of the show in a black depression, occasioned by the death of her mother. When she tells a brash young obstetrician that she is expecting, he retorts that the grieved mind can play curious tricks on the body and whips out his prescription pad. The depression gets deeper, until Leenie is reexamined after a fortuitous automobile accident. Lo! A baby is truly on the way. But after all the pills, what kind of baby?

In the second hour, Leenie wrestles with the horrible possibilities, her Catholic conscience, patronizing relatives and inept doctors before concluding . . . well, nothing. Reluctant, perhaps, to take an outright stand on the abortion issue, the program leaves her up in the air. After so much anguish, the ending--it is Leenie's body, her choice--is a big, fat dramatic cop-out.

Even in stillness, Redgrave has a gravely expressive face and she's always been good at projecting inner torment. But neither she nor her fellow performers (the late Jack Albertson, as her father; Joseph Campanella, as her burly husband; James Naughton, as the shallow obstetrician) can transform a script that roasts more chestnuts than an open fire. Lines like, "Life throws us a curve, the game goes on, we'll manage," are not calculated to bring out the best in actors.

Redgrave should have packed up her talent and taken it elsewhere.