For two days this fall, come what may, some 70 world leaders will sit down at the United Nations and talk about breast-feeding, diaper rash and fundamentals like that. The tension in the Middle East has made the World Summit for Children more desirable to officials who previously didn't seem particularly moved by the fact that 40,000 children die every day of preventable diseases and malnutrition.

George Bush and Mikhail Gorbachev, both of whom have spoken of the moral dimensions of the tragedy, are expected to attend and to speak. Saddam Hussein offered to send his health minister, but was turned down -- only heads of state need apply. Benazir Bhutto, decanted from her job as prime minister of Pakistan on Aug. 6, has also lost her job as co-chair (with Canada's Brian Mulroney) of the summit, but the show will go on. Moussa Traore of Mali will take her place.

The chance of bilateral chats with heads of state at a time of a threatened war has proven irresistible, and some 10 countries who expressed no previous interest have signed up in the last two weeks. By Sept. 29, the day the summit is convened, the question of war or peace in the Middle East will probably be answered. If it's war, the summit becomes more urgent. Among the millions of refugees to be generated, children are the most vulnerable.

Can the two-day session be something more than a mega-photo opportunity/traffic jam? Will informal negotiations on other questions considered more pressing by the delegates overwhelm the small subjects of the conference? Coordinator Michael Shower thinks it will. Many countries, including the United States, are planning to use the summit as a way to lever health care reforms at home. Planning meetings are being held all over the world. In India, for instance, conferences and seminars about specific health problems to be raised at the summit are taking place in every state. The city of Baltimore is observing the onset of the summit with a major vaccination program.

An organization called World Summit for Children Candlelight Vigil is planning a series of rallies nearer the time of the meeting to focus public attention on the scandalous neglect and abuse of little children.

And Rep. Tony Hall (D-Ohio) is planning to introduce a bill that will ensure that more than hot air will emanate from Turtle Bay. He will offer a bill that would pay the U.S. share of a U.N. effort to distribute food and immunization that should reduce by a third the 15 million annual death rate of children under 5. He would also use some of the initial $275 million appropriation for the WIC (supplemental food for women, infants and children) program, which currently serves just half of its eligible constituency.

Hall makes the argument that if 40,000 children are dying every day, cost should not be the first consideration, even in these days of deficits and Gramm-Rudman-Hollings. And to be practical, preventive health measures save money. It is much cheaper to feed the baby during the mother's pregnancy. The WIC program costs approximately $10 per week per mother. It costs $1,400 a week to keep a low-weight baby in the neo-natal ward. Between 1987 and 1988 in the District, the infant mortality rate rose from 19.6 to 23.2 per thousand, a mortifying statistic for the capital of the world's most developed industrial nation.

Things are even worse in developing countries. In the UNICEF report, which precipitated the children's summit, UNICEF Executive Director James P. Grant writes, "It is the greatest condemnation of our times that more than a quarter of a million small children should still be dying every week of easily preventable illness and malnutrition . . . . Such facts shame and diminish us all."

What maddens health professionals is that the cost of preventing tragedy is so trifling. Take diarrheal dehydration, which kills almost 7,000 babies a day. It can be cured by packet of proteins and salt that costs 10 cents. Consider breast-feeding. It costs nothing, and it is the finest nutrition the baby could have. But health workers are not sufficiently trained to extol its virtues, and too many Third World mothers turn to formula feeding, which might not be fatal if there were clean water to mix it with.

These matters will be discussed by the most important people in the world. The sessions will open with a film showing the sad state of these most vulnerable beings. They will close with a long overdue Declaration of Children's Rights, to be read to the assemblage by children.