Divorce has become a specter that haunts the modern American family the way the plague once spooked Europe -- and with good reason. In 1970, there were 2 1/2 million children living with a single divorced parent; by 1990 the number is expected to double.

Even if a child lives in a placid home (wherever that is), he has seen divorce strike so many friends and neighbors, and often so unexpectedly, that he doesn't feel quite safe any more. Each overheard argument can seem like an omen; each scene a crisis. And if a divorce does occur, it is a trauma that will rock him for years.

Whether you've endured a divorce or not, your understanding of it, and how it affects children, will be greater if you see the one-hour TV special on Channel 26 at 6 p.m. this Sunday -- "Mister Rogers Speaks With Parents About Divorce."

When watched with your child, it is the ideal springboard to talk with him about his own fears and about the feelings of guilt and anger and grief that divorce brings to all ages.

The show is a forum led by Susan Stamberg, the thoughtful co-host of "NPR's "All Things Considered"; dr. Earl Grollman, a rabbi who uses a divorce ceremony as part of his counseling service, and Fred Rogers, that gentle man who has for 26 years talked to sweetly and softly to children on television.

The three talk among themselves, listen to parents in the audience describe how they coped with divorce and show film clips of conversations with children, both with and without their divorced parents.

Through it all comes the overwhelming pain of divorce, the fatigue, the sense of worthlessness that strikes both parents and children and the need to have some impartial person guide them through the grieving process.

As they found, the "medicine of time" only works if the time is used creatively and that means counseling and support groups. Without this assistance, it may take years -- or forever -- for parents to feel like loving people who also are capable of being loved. This is true of the children, too.

Even with counseling, the participants agree that it takes at least two years to deal with the anguish of divorce well enough to talk easily about it, as the parents and children on this show are able to do. Studies show that only a fourth of the parents and children involved in a divorce can cope well with the idea, even five years later.

Some divorces are reasonably painless, of course, but according to Grollman, this only happens if there are no children or money to divide and both husband and wife have someone else to marry.

Mister Rogers (who also is a Presbyterian minister) and Dr. Grollman recognize that divorce, painful or not, may be the only sensible solution, but when children are involved they hold some views that may be rather unpopular today. For Mister Rogers, parents "have a responsibility to their children" to stay married, "unless," says Grollman, they "can't stand it any more and can't grow any more."

Many people, however, rush into divorce, because they're "just not happy," but as Grollman points out, "If you don't have fights, you don't have a marriage."

If nothing else, their point of view reminds us thatlife isn't quite as simple as the women's magazines would have us believe.

For back-up to the show, there's a free booklet called "Mister Rogers Talks About Divorce," which you can get by sending a long, stamped self-addressed envelope to Mister Rogers, Pittsburgh, Pa. 15213. For counseling in this area he recommends Family Service Assn., 1819 H St. NW, 659-8732, and the Divorce and Marital Stress Clinic, 1925 N. Lynn St., Arlington, Va., 528-3800.

Divorce also will be the theme of "Mister Rogers' Neighborhood" Feb. 16-20. The program for preschoolers is shown at 11:30 a.m. each day on Channel 26.

You'll find the subject is delicately woven into a small part of the show. Each day carries a different message, gently told: that people aren't happy all the time; that a quarrel doesn't mean a divorce; that the child hasn't caused the problem (which is still mighty hard for the egocentric preschooler to believe); that parents may divorce each other, but never their children, and that parents and children need to know how each other feels -- and why.

You may think "Mister Rogers' Neighborhood" is too slow for your child, especially if he is a live-wire, but some psychologists find it is the best of all children's shows. Jerome and Dorothy Singer of Yale recently discovered that the short, flashy segments on such shows as "Sesame Street" cause a shorter attention span in young children as well as the same aggressive behavior caused by wild game shows and cops and robbers.

In contrast, "Mister Rogers" is as slow and easy as a walk in the woods and this is the tempo that gives a child time to reflect. The more important the subject, the more time he needs to assimilate it.

The daily shows should do for little children what the Sunday-night special does for adults: give them the information -- and the security -- to talk about divorce without being embarrassed or afraid. You'll find it's much easier to decode your own child when someone has given you the cipher and Mister Rogers is a quiet master of cryptology.