NEW YORK, SEPT. 26 -- About 80,000 children around the world will die this weekend even as more than 70 world leaders, including President Bush, converge on the United Nations for the first World Summit for Children.

They will die mostly from measles, tetanus, whooping cough, pneumonia or dehydration caused by diarrhea -- maladies for which simple, inexpensive treatments exist. This will happen during an event that is to focus on problems of children everywhere and which U.N. officials say will be the largest gathering ever of heads of state.

They are expected to come from Uganda and Uruguay, Albania and Zimbabwe, even Kuwait and Saudi Arabia. Cuban leader Fidel Castro is expected, but Soviet President Mikhail Gorbachev is not.

"When children are involved, politicians like to have their pictures taken with them," said James P. Grant, executive director of the United Nations Childrens Fund (UNICEF). "But when push comes to shove, it's usually poor mothers and children last."

While the government leaders attend banquets and briefings, the children will continue dying, although most treatments for their ailments were developed long before the United Nations celebrated the "Year of the Child" a decade ago.

"It is as though we discovered the cure for cancer 20 years ago and didn't bother to use it," a UNICEF official said this week.

For these reasons, Grant has dubbed the 90s the "Decade of Doing the Doable," and UNICEF has set what he said are realistic goals for the year 2000: immunizing 90 percent of young children, reducing infant mortality by one-third and maternal mortality by one-half, eradicating polio and ensuring that every child of each sex has access to a primary education.

Although such goals often go unmet, U.N. officials are expressing confidence that this time could be different. They cite a new international treaty called the Convention on the Rights of the Child, often referred to as the "Magna Carta" or "Bill of Rights" for children. It was endorsed by the U.N. General Assembly after 10 years of debate.

Already, 109 nations have signed it, and 42 have gone a step further and ratified it, meaning that their legislatures or decision-making bodies have passed it into law. The document became international law last month.

Bush has not announced whether he will bring it to the Senate for ratification.

Such inaction has prompted advocates for children in the United States, such as the Children's Defense Fund, to note that this country is hardly a model of child health and welfare. The United States ranks equal to or lower than some Third World countries in many indicators comparing children's quality of life worldwide.

For example, the United States ranks 19th in infant mortality and 21st in mortality of children under 5. Almost one in every four American children under 6 lives below the poverty line, according to the National Center for Children in Poverty at Columbia University.

Grant pointed out that Costa Rica, Jamaica and Sri Lanka, for instance, "all have infant-mortality rates lower than Washington, D.C.," whose rate is highest among U.S. cities and states.

U.S. advocates for children have insisted that this weekend's conference focus not only on developing countries but also on industrialized countries with less than exemplary records on child welfare.

UNICEF officials estimated that the cost of an international mobilization to meet the goals of the "Decade of the Doable" may come to $2.5 billion annually.

"It's a lot of money," Grant said. "But on the other hand, it is what the American tobacco companies spent on advertising last year, what the Russians spent on vodka last month and less than what the world spent on the military yesterday. This is half of what we spend in the U.S. on pet food each year.

"To say that the world can't afford this kind of resource shift is to say we really don't care," he said.

The week leading to the summit has revealed an optimism and enthusiasm that children's advocates say has not been seen for more than a decade. On Monday, more than 250 children from countries worldwide, many of them children of diplomats, gathered for a Children's International Congress across the street from the United Nations. They drew up lists of demands.

"By telling the grownups what we want, not what they think we want, we're going to fight for children who aren't as fortunate as we are," said Nessrim Minessy, 10, an Egyptian living with her family in New Jersey, as she skipped around the auditorium with newfound friends from Angola, Argentina and the United States.

Marvin Sochet, who with his wife founded Kids Meeting Kids, which organized the congress, said, "All laws are violated left and right. That's why the kids are meeting, to make sure their countries adhere to the convention when it is passed."

One by one, groups of children stepped up nervously to a microphone to read the lists they had written, usually in crayon, of what amounted to a bill of rights.

"We need food, water, clothing, a house, a bed, medicine, a school, good air, love and friends," read Paul David Mburi, 7, of Tanzania, "and not to have guns or bombs."

Some members of Paul's group, the youngest, do not yet read. But they were the only ones who wrote on their list the word "lawyers."