Ever on the run, at least on jaunts to the United States, Mother Teresa made two stops on her day in Washington last week. In the morning at the White House, she asked Ronald Reagan to help find space in New York for a center to treat AIDS victims. Her religious order, the Missionaries of Charity, operates a 14-bed facility in Greenwich Village.

In the afternoon, the 75-year-old Catholic sister, speaking to an audience of 400 members of the National Council for International Health, gave awards to three developing countries for their work in saving the lives of children through early health care.

The first stop received more publicity than the second. One was public relations, the other human relations.

The attention should have been reversed. The medical story of the year, and perhaps the decade, is likely to be the successes being quietly recorded by nurses, doctors and health-care workers who are immunizing Third World children against infectious diseases. Globally, some 3.5 million children die every year from measles, polio, diphtheria, tuberculosis, neonatal tetanus and whooping cough. All are vaccine-preventable.

Last year, the United Nations Childrens Fund (UNICEF) said in its "State of the World's Children" report that "a low-cost revolution" is beginning through oral rehydration therapy and immunization programs.

If that's true, one of the revolutionaries is Dr. William Foege, 50, president of the American Public Health Association and former director of the Centers for Disease Control. Two years ago, Foege, who has done field medicine in rural India and Nigeria, helped organize the Atlanta-based Task Force for Child Survival. Sponsored by such groups as UNICEF and the World Health Organization, it has set 1990 as the goal for universal immunization.

Foege believes that "Unusual progress has occurred in the last two to three years. The number of children dying from vaccine-preventable diseases has gone down from about 5 million a year to 3.5 million a year."

Foege insists that the death rate will go lower once the inexpensiveness of immunization is known. The costs for treating all children of the Third World, he estimates, would total no more than $1 billion, or less than $10 a child. "If you could divert only two minutes' worth of the global weapons budget, you could immunize all the children born that day for their lifetime," he says.

The countries honored by Mother Teresa and the National Council for International Health were Egypt, Colombia and Turkey.

*In Egypt in 1981, only 5 percent of Alexandria's mothers knew about oral rehydration therapy (ORT) -- the solution of salts and water that combats diarrheal diseases. Only 1 percent had tried it. Today, through a combination of effective delivery strategies, outreach services and publicity, more than 90 percent of the mothers know of ORT and 50 percent have used it for their children.

In Colombia, the nation's largest newspaper, El Tiempo, joined with the national broadcasting network, Caracol, to jolt the population into action. As a result, more than 800,000 children were immunized in only a few months. It's estimated that about 1,000 deaths a week were prevented.

In Turkey, with President Kenan Evren's government vaccinating children against polio on the first of three 10-day national immunization campaigns that began last autumn, nearly 80 percent of the young have been covered.

By coincidence, Mother Teresa's visit to Washington put her at an intersection in which the American public's concerns about diseases appear to be moving in different directions. AIDS, a new blight with no known cure, has received massive amounts of publicity. About 11,700 AIDS deaths have been reported. Yet at the same time, it passes almost unnoticed that more than three times that number are dying every day from children's diseases for which cures are known.

The campaign to find a vaccine for AIDS is crucial, but the excitement of pursuing a mystery disease shouldn't take precedence over dispensing proven cures for known diseases.