The parents of an 18-month-old boy whose system can only absorb nourishment from human breast milk are asking nursing mothers to donate milk.

Marion Forrest, who only weighs 11 pounds -- about half the normal weight for his age -- consumes about 11 quarts of breast milk a week, approximately half the amount used by all the other babies in Georgetown University Hospital's intensive care nursery, where he is now a patient.

A breast milk bank at Georgetown, the only such storage facility in the area, is keeping up with the baby's needs while he is in the hospital, but will not be able to continue supplying him when he returns home.

Physicians do not know precisely what is wrong with the child, who has spent most of his 18 months in the hospital. He has proved to be allergic to virtually every kind of milk and nonmilk formula on the market, and does not absorb enough nourishment from solid food for him to be fed that way.

The Georgetown milk bank, supplied by nursing mothers in the hospital and mothers whose babies have been discharged, keeps the milk either frozen or refrigerated. The milk is generally used for premature infants who benefit from the antibodies found in breast milk.

But the supplies in the milk bank are needed for patients in the hospital, and when Marion Forrest is discharged -- a yet-to-be determined date -- his mother will be unable to keep up with his needs.

Those interested in donating milk are asked to call Sandra Scott Forrest, the baby's mother, at 249-6197, or Marsha Kurtz, a Georgetown volunteer, at 320-4071.