Q. Jenny, a 5-year-old, is ecstatic, writes a Silver Spring mother. "She's going to have a birthday in May and she talks about it constantly: who's coming to the party; what games they will play; what kind of cake they will have, and, by all means, what kind of toys she wants. This is what bothers me. She has so many things now, and she doesn't even take care of them."

A. The more toys a child has, the less they take care of them, except for one or two favorites. That doesn't stop them from wanting more, however.

At the top of Jenny's list are surely the toys her friends have and the toys advertised on television, which are usually the same.

You can handle this easily, we've found. You say the best toys aren't advertised, and you only want your child to have the best. Who could argue with that?

To find out what presents to buy, sort through her toys and her clothes too. Pack up the outgrown and the out-of-season; repair what can be mended and throw away the hopeless.

If you want your child to take care of what she has, she should have sturdy toys that can take rough play. Otherwise she will think of herself as a destructive person. To help your child appreciate what she has, put away a third of the toys that are left, rotating all but a few treasures every six to eight weeks, for to a child -- like anyone else -- less is more.

In the process of taking this inventory, you'll focus so hard on the way your child plays you'll have a new insight into her real preferences.

"Thanks so much for the column on infant screening for retardation, and for the mention of the Infant Metabolic Diagnostic Laboratory," writes a spokesman for the lab.

"To set the record straight, however, only our newest 'lab within a lab' is dedicated to Jacob Burns. The ohter equipment, some of which has been in use for as long as a year, was paid for by the Public Welfare Foundation; Clipped Wings; the Eugene and Agnes E. Meyer Foundation; the Max and Virginia Dreyfus Foundation, Ind., and by private donations.

"The next money we get will help us complete the research and development of the two new tests which may identify half of all retarded babies born -- so treatment can begin -- rather than the 1/2 of 1 percent that can be picked up now."

Patricia O'Connor, president of Beech Tree School PTA, Falls Church, says the school has a new cued-speech program for hearing-impaired children and it is a "great success."

"The new program has only six children -- although it can be expanded -- and we are happy to have it at Beech Tree.

"The children have their own classroom and teacher, but they are mainstreamed as much as possible. Hearing children take great pleasure in learning to 'cue' with their deaf classmates and many of our teachers have learned the system too, so they can teach these children in their own classrooms.

"I believe it is a positive experience for all of our children, hearing and deaf, and I recommend 'cued speech' enthusaistically."

Another response: "You state that parents of hearing-impaired children need help, too, and that is to true. The Alexander Graham Bell Assn. for the Deaf assists these parents in many ways. I hope they call us at 337-5220."

From Alexandria comes an annoyed reader who feels we booted a recent reply. Like an earlier correspondent, she felt the Three who had turned into a "monster" was reacting to nursery school.

"As a teacher, I have observed and worked in nursery schools where I would not leave my dog. Poorly paid, frequently changed, inexperienced people would treat children one way when parents were there and another when they were not. I would never enroll my children in such establishments.

"You seem to have some pitfalls in proclaiming yourself an expert, to answer as rudely as you did."

A. This letter is not what the Landers lady would call a day-brightener.

We're not quite sure why our answer seemed rude, but apologize just the same. As for the nursery school, we though it went without saying: A parent only puts the child in a school after checking with other parents, observing teachers carefully and seeing if the children look happy to get there.

If the environment is good -- or even pretty good -- a Three will profit more by being with other children those nine hours a week than he will by being with his parents on a non-stop basis.