LONDON (AP) _ Three-year-old Leoni Keating was raped, thrown into a ditch and left to drown. Toddler Tyra Henry was bitten 57 times and battered to death. Three- year-old Heidi Koseda starved to death in a locked bedroom.

This year, the names of Leoni, Tyra, Heidi and dozens like them have become well-known as Britain confronts the growing problem of child abuse and child murders.

Every week in Britain, a child is killed by his parents or guardians. Every other week, a child is murdered by strangers or other relatives, according to the National Society for the Prevention of Cruelty to Children (NSPCC).

In the last six years, the NSPCC said reported incidents of physical abuse against children under 15 increased by 70 percent - with the sharpest increase in 1984 involving sexual abuse.

Marital discord and unemployment are the prime underlying causes for child abuse, the NSPCC said.

''We fear that unless urgent action is taken at every level, more and more children will be exposed to danger,'' said Lord Tonypandy, former speaker of the House of Commons. He launched a child safety campaign in September on behalf of the National Children's Home charity.

According to the Children's Home, 2,000 children a week see their parents separate, 1.7 million live in families that are on or below the poverty line and 400 are made wards of the state each week because of ill treatment or neglect.

Drug addiction among children has tripled in the last three years, and 83,000 families are homeless - 73 percent with children.

The latest government statistics showed 86 children under the age of 16 were killed in 1984, including 54 under the age of five.

''We have got a crisis on our hands in Great Britain as far as kids are concerned,'' said John Gray, appeals director of the National Children's Home.

''The love has gone out of parenthood in many, many cases. And that is why it's coming to a head, especially in these past weeks, with the awful deaths, the muggings and the neglect.

''It all goes back to the home. If we don't give children love, a bit of affection and cuddling, we're not going to have a society tomorrow,'' he said in an interview.

''The unloved grow up to be the unloving - that's why we have so many people growing up to be battering parents,'' said Dianne Core, who founded a group called Child Watch six months ago in northeast England to campaign against child abuse. ''We are bringing up people who can only express themselves through violence.''

A 1979 study by Dr. Tony Bennett, a former Royal Navy pediatrician, found mothers who battered their children to be generally young, of low educational achievement and were themselves victims of sexual abuse in childhood. Fathers were generally small, poorly educated, and had often been abused as children.

The typical couple had married young, against the wishes of their parents, had few friends and lived far from their families in increasing misery. The children were often unplanned and premature, the study found.

Of physically injured youngsters studied by the NSPCC, fewer than half lived with their natural parents while 28 percent lived with their mother and a substitute father. Of sexually and emotionally abused children, 31 percent lived with their real parents while 40 percent lived with substitute fathers.

The recent cases that have made headlines in Britain bear out the studies.

Leoni Keating disappeared from a campsite after she was left alone by her mother, a battered wife estranged from her husband. Tyra Henry, only 21 months old, was battered by her father, who left her at a London hospital where she died, and then went to celebrate his 20th birthday.

Heidi Koseda was locked in a filthy, cold room by her 26-year-old stepfather, a man of subnormal intelligence who said he decided to stop giving her food after she took some candy from a cupboard. The tragedy was compounded because an NSPCC inspector faked a report saying she was alive and well when she was already dead.

And there are more. Six-week-old Hannah Newman, whose stepfather fractured her skull so badly that it dislodged her brain; 4-year-old Christopher Stock, who was bitten and beaten to death by his mother and her lover; and 6-month- old Michael Brophy, who was blinded by corrosive fluid poured in his eyes and whose father leaped to his death while on trial for blinding him.

''Our attitude towards children in this country is really a disgrace -- it's as though our attitude is one of rather disliking children, accompanied by periods of panic, as at the moment,'' said Dr. David Pithers of the Center for the Study and Development of Child Care Practice, a research body associated with the Children's Home.

The National Children's Home urges parents to protect their children by following a six-point program: Be generous in the time they give their children, make them feel valued, explain things happening in the family that affect them, provide detailed rather than vague warning about possible dangers, make sure they feel secure and make sure they have fun.

Conservative lawmaker Geoffrey Dickens has promised to reintroduce a bill during the next session of Parliament that would ban organizations advocating sex with children and make it illegal to possess child pornography. ''It has been a dreadful summer of child abuse and murders,'' he said.