An obscure but influential program that gave detailed public health information to about half of the world’s nations will fold as a result of the Trump administration’s freeze on foreign aid.

With funding from the United States Agency for International Development, the Demographic and Health Surveys were the only sources of information in many countries about maternal and child health and mortality, nutrition, reproductive health and H.I.V. infections, among many other health indicators.

The surveys collected data in 90 low- and middle-income nations, which then used the information to set health benchmarks at the local, national and global levels, including the 2030 Sustainable Development Goals adopted by member countries of the United Nations.

On Tuesday, the program’s administrators learned that it was being “terminated for the convenience of the U.S. Government,” effective immediately, according to an email viewed by The New York Times. They were ordered to “stop all work, terminate subcontracts and place no further orders.”

The Trump administration is dismantling U.S.A.I.D.; thousands of layoffs are expected in the coming days. Without future surveys, it will be nearly impossible to measure the impact of those foreign aid cuts on citizens in nations without substantial health infrastructure.

Some global health experts reacted to the program’s demise with dismay.

“It’s really challenging for me to understand how you could implement thoughtful programs in public health and monitor progress toward strategic goals if you don’t have the kind of data that are available from the D.H.S.,” Win Brown, a demographer at the University of Washington, said.

“You can’t keep track of what’s going on, you can’t form strategies, you can’t make adjustments based on how your data are changing,” he added.

It was unclear what might happen to the research that has been collected over past decades, or to the ongoing survey projects in 25 countries. “We need to figure out a way to salvage that data, and I think that’s feasible,” Livia Montana, the program’s technical director, said.

The surveys have been conducted since 1984. The funding totaled about $500 million over five years, about half of which came from U.S.A.I.D. and half from other donors, including the nations themselves.

Some countries, like India, had almost entirely taken over the financing of their own surveys. The research is widely seen as indispensable.

“The impact of these disruptions will reverberate across local, regional, national and global levels,” a group of dozens of experts warned on Feb. 13.

Some United Nations organizations assess child and adolescent health or census data in some countries, while others measure household income or agricultural output.

But the Demographic and Health Surveys, collected every five years, recorded all critical aspects of household health, including mortality data, height and weight and nutrition status of children and adults, education and literacy, as well as access to clean water and mobile phones.

“Malnutrition indicators are among the most important,” because they can reflect a range of societal factors, Dr. Montana said. The surveys also separately evaluated malaria indicators and health facilities.

Estimates of maternal and child mortality are crucially important in countries that do not have good death registration systems. The surveys also measured family size, which can indicate the availability of family planning but also reflect broader societal factors, including access to education for girls.

Dr. Brown has used the surveys, for example, to compare contraceptive use among women in countries like Egypt, Pakistan and India over decades. “In a survey like D.H.S., you’re on the ground talking to real people, on the stoop of their real houses in real communities,” he said.

Like other projects funded with foreign aid, the program was under a stop-work order before the termination. All but 11 of its staff of 80 were placed on leave without pay, and its relationships with contractors ended a few weeks ago.

Informed of the halt, some national governments expressed concern and empathy, and several asked if they could pay to finish the work. Others took it in stride, Dr. Montana said.

“It’s sort of like they have experienced more of this kind of thing where political winds change right away,” she said.