Two weeks into President Trump’s sweeping freeze on foreign aid, H.I.V. groups abroad have not received any funding, jeopardizing the health of more than 20 million people, including 500,000 children. Subsequent waivers from the State Department have clarified that the work can continue, but the funds and legal paperwork to do so are still missing.

With the near closure of the American aid agency known as U.S.A.I.D. and its recall of officers posted abroad, there is little hope that the situation will resolve quickly, experts warned.

H.I.V. treatment and services were funded through the President’s Emergency Plan for AIDS Relief, or PEPFAR, a $7.5 billion program that was frozen along with all foreign aid on Mr. Trump’s first day in office.

Since its start in 2003 during the George W. Bush administration, PEPFAR has delivered lifesaving treatment to as many as 25 million people in 54 countries and had enjoyed bipartisan support. The program was due for a five-year reauthorization in 2023; it survived an effort by some House Republicans to end it and was renewed for one year.

Without treatment, millions of people with H.I.V. would be at risk of severe illness and premature death. The loss of treatment also threatens to reverse the dramatic progress made against H.I.V. in recent years and could spur the emergence of drug-resistant strains of H.I.V.; both outcomes could have a global impact, including in the United States.

The pause on aid and the stripping down of U.S.A.I.D. have delivered a “system shock,” said Christine Stegling, a deputy executive director at UNAIDS, the United Nations’ H.I.V. division.