Infant death rates in many less developed countries are expected to drop significantly as a result of a campaign to improve child health care launched two years ago, the United Nations Children's Fund has reported.

"Many thousands of lives are being saved," Unicef said in its report, "The State of the World's Children 1985." In many Third World countries "there is now a realistic basis for hope that, over the next 10 or 15 years, infant death rates will fall by as much as 5 percent or more a year," the report said.

The Unicef program for improved nutrition and health care stresses oral rehydration therapy, a technique to combat dehydration with a solution of water, salt and glucose. The technique, which can be administered to children by their parents, could save most of the 4 million children who die each year from dehydration, according to the Unicef report.

The program also calls for breast-feeding through the first six months of a child's life, a course of immunization against a half dozen diseases, which costs about $5 per child, and growth monitoring to spot malnutrition.

"Breast-feeding is a natural 'safety net' against the worst effects of poverty," Unicef said. "Unless the mother is in extremely poor nutritional health, the breast milk of a mother in an African village is as good as the breast milk of a mother in a Manhattan apartment."

Unicef's report listed several success stories in its efforts to improve the health of children:

* An "accelerated health program" in Pakistan -- where a half million children had been dying each year from diarrheal dehydration and "immunizable" diseases alone -- increased the immunization rate from 5 percent to nearly 50 percent and produced 30 million packets of oral rehydration salts.

* Infant and child deaths in Baguio in the northern Philippines have been reduced by 50 percent during the past five years.

* More than 800,000 children have been immunized during three National Vaccination Days in Colombia.

* In Brazil, 2 million children under age 2 were vaccinated against measles; 1.5 million were immunized against diptheria, whooping cough and tetanus; almost all of the nation's children were protected against polio.

* In Tanzania, a campaign based on oral rehydration therapy and growth monitoring has been launched as the first stage of a program aimed at halving the death rate of the 50,000 children living in 167 villages of Iringa Province.

* The infant mortality rate in Algeria's Cheraga district has been cut from 103 per 1,000 to 43 per 1,000, or about 60 percent.

Unicef's report emphasized the importance of educating poor women in Third World countries, pointing out that "a child born to a mother with no education has been shown to be twice as likely to die in infancy as a child born to a mother with even four years of schooling."

The campaign also is attempting to educate parents about the importance of spacing their children. The incidence of infant and child mortality has been found to be twice as high when the interval between births is less than two years, Unicef said.

"Most of the 40,000 young children who are now dying each day are dying not because they lost a battle but because they lost a war -- a long, losing war against the sheer frequency of the assaults on their growth during their vulnerable years," the report said. "Each infection, whether it be measles or diarrhea or whooping cough, lowers the child's nutritional status and leaves the child weaker and more susceptible to further infection."

The report was released Wednesday in London by James P. Grant, Unicef's executive director.