Sixth-grader cools the high jinks and settles down to writing plays

For the second year in a row, Christian Freitag has written a prize-winning, sensitive play on environmental issues - a fact that bodes well for his future as a playwright, says Doris Indyke, producer of the Children's Radio Theatre, which granted both prizes.

Chris is a sixth-grader who became a playwright as an alternative to busting water fountains.

''We got a call from the school about a water fountain,'' says John Freitag, a bearded social worker from Valparaiso, Ind. ''Apparently they'd installed this new fountain. Then Chris got a hold of some BBs and tried to demonstrate the principle of hydraulic energy by stuffing them down the water spout and shooting them back out. Well, it worked really well for the first two BBs,'' he says, pausing dramatically.

School authorities told the Freitags that their son ''was apparently finishing his schoolwork by 10:30, getting bored, and getting into trouble.''

As an antidote to his high jinks, one of Christian's teachers showed him a tiny advertisement for a playwriting contest sponsored by the nationally syndicated Children's Radio Theatre (CRT) in Washington, D.C. That was last year , when Christian, then a fifth-grader, won his first national contest with what CRT spokeswoman Indyke calls a ''thoughtful, relevant play'' about two important topics: gasoline and greed. Called ''The Pill That Almost Saved the World,'' the play pits a child who discovers a method for turning water into gasoline against a host of people wanting to exploit his formula for their own profit.

Now he's back at another CRT awards ceremony, this time with a winning sequel called ''The Lucky One,'' a witty and poignant play Ms. Indyke says is ''even better'' about another relevant topic: endangered species. In it, a child named Chris sets out, with help from parents John and Susan, to save the Black Billed Dinto from extinction. He manages to save one, but his efforts to protect the species fail, demonstrating, he says, ''that it's necessary for all of us to work together.''

He's a serious-sounding kid with straight hair and serious ideas: ''I think we should do away with jealousy and greed, live in peace, and help each other, not just kill. We're always trying to better the Soviet Union, and they're always trying to better us - it's just jealousy,'' he says.

Yet his play sparkles with an underlying humor:

John: Gosh, am I glad that Chris decided to throw away the chemistry set I bought him last Christmas. It was really getting to be a menace. Things have been a lot quieter around here lately.

Susan: Not to mention a lot safer! Now we don't have to worry about our house smelling like rotten eggs or our garage burning down.

John: Well, that's true, but it was a learn. . . .

Susan: John! Don't you dare say it! I don't know what made me angrier, Chris chemically destroying our house, or your excuse that it was all a learning experience.

Learning comes easily to Christian, an all-A student. ''I use a line my father told me,'' says Mr. Freitag: ''There's no such thing as D's and F's; C's mean you showed up in class; B's are acceptable, but are they really your best effort?''

This advice has had a different effect on his children than it had on Mr. Freitag, says Chris. ''My parents seem to wonder where they got my brother and me. They never got straight A's like we do,'' he reports.

The brothers seem to follow each other's lead, say the parents. Fourteen-year-old Jason started writing in his elementary school's Young Author's program years ago, and Chris followed his example in second grade - winning the contest every year since. And now Jason has taken up playwriting - and has taken one of the four awards given this year, picked out from more than 1,000 entries to CRT's Henny-Penny Playwriting Contest.

Second grade was pivotal for both sons' writing careers, say the Freitags. ''They both had the same teacher, Delores Kraisinger,'' says their mother, Susan - also a social worker - ''and she got them going on writing stories, books, and poetry.''

''She was my inspiration,'' Chris says of this favorite teacher.

But there's more to the Freitags than writing. Chris cares for a bird, a dog, and many fish at home. He's also a state wrestling champion and plays baseball and soccer. Chris says his favorite subject is science and that he doesn't want to be a writer when he grows up because he wants to do something that ''will make the world better.''

Like being an astronaut. ''It has everything a job should have - it helps people, it's fun, and the pay is good,'' he says.

''They set their own goals, and we try to give them positive support,'' says Mrs. Freitag, who admits that ''some people think we push them more than we should. We set high standards of excellence.'' But what she thinks accounts for her children's success, she says, is knowing that ''we love them with all our hearts. And we love each other - I think that's important.''