Public health experts have raised serious questions about the effectiveness and international impact of the Reagan administration's plan to require testing of all immigrants to the United States for exposure to the AIDS virus.

They predict that the plan to test about 400,000 immigrants a year, if it functions as similar disease-control measures in the past, is unlikely to stem the spread of acquired immune deficiency syndrome. Instead, they said it may provoke retaliatory policies from other countries and rapidly generate a black market in false test certificates. They also raise concerns about the availability and accuracy of tests in other countries for infection with the AIDS virus.

"It's a terrible idea," said Dr. D.A. Henderson, dean of Johns Hopkins School of Hygiene and Public Health, and former coordinator of the successful worldwide effort to eradicate smallpox.

Administration proposals for routine testing for infection with the AIDS virus have provoked broad debate about issues of confidentiality, cost and the role of testing in preventing spread of the disease. But the plan to test immigrants has met with less public criticism than those affecting other groups because it is widely viewed as a move to safeguard U.S. citizens, with no domestic repercussions.

The proposal to include a negative blood test for antibodies to the human immunodeficiency virus (HIV) as a requirement of entry for immigrants was published in the Federal Register June 8, eight days after President Reagan announced the plan in a speech here on the eve of the Third International Conference on AIDS.

Last Wednesday, AIDS was officially added to the list of eight "dangerous contagious diseases" that constitute medical reasons for denying an immigrant visa. The proposed rules would further amend the list, substituting "HIV infection" for AIDS. Because infected individuals frequently have no symptoms and confirmatory tests are needed if an initial blood test is positive, immigrants applying from other countries would have to be tested before coming to the United States.

The administration is moving rapidly to put the plan into effect. Written comments on the proposed rules are due by Aug. 7, and the final rules will be submitted "shortly after that," according to Charles McCance, acting director of the federal Centers for Disease Control's quarantine division. In an amendment to the supplemental appropriations bill for the current fiscal year, Congress voted to require that immigrant testing for HIV be implemented by Aug. 31. That bill is awaiting the president's signature.

Henderson, the Johns Hopkins dean, said he had been told that only about 40 countries have the capacity to conduct HIV testing. He predicted that the new requirement would generate an immediate black market in false test certificates and would prompt many other countries to adopt similar testing policies, but would be ineffective in preventing the spread of AIDS.

He compared the plan with requirements for smallpox vaccination as a condition of entry to many countries in the past, before the disease was eradicated. "Did this keep the disease out? No, it didn't," he said. "Quarantine measures have never been found to work particularly well in preventing spread."

Henderson said he had been told the State Department estimates that about 250 would-be immigrants would test positive for HIV infection annually. The Public Health Service estimates that about 1.5 million Americans are infected. Henderson added that inadequate quality control of HIV testing in many countries could result in significant numbers of false-positive results, with disastrous consequences for test recipients. "The hysteria in countries where there are very few cases is enormous," he said. A person with a false-positive test "could very well become a pariah."

"The potential for massive retaliation" by other countries if the United States begins to test immigrants "is simply mind-boggling," said Dr. June Osborn, dean of the University of Michigan School of Public Health. "We are so much more exporters than importers" of AIDS.

Court Robinson, a policy analyst with the United States Committee for Refugees, said he thinks the testing policy could discourage other countries from granting temporary asylum to refugees because of fear of being permanently burdened with any who tested positive.

"It plays onto the xenophobic attitudes of other countries and it plays onto the same fears here," he said. "Frankly, I don't see why other countries won't start doing the same thing for Americans. Then you're going to hear an outcry on the part of the business community and tourists."

Gary Bauer, Reagan's domestic policy adviser, discounted reports of opposition to the plan. "The administration is moving ahead because a decision has been made," he said. But he added that the proposed regulations governing testing of immigrants "are open to be changed. Our position is, if there is a problem, it's not an insurmountable problem."

Bauer said decisions by other countries to require testing of immigrants and visitors would take place independently of the proposed U.S. policy. "My own view is that if other countries require such tests before tourists can come in, I don't see why anybody has a legitimate right to object," he said.

Dr. C. Everett Koop, the U.S. surgeon general, who has not opposed mandatory testing for immigrants and federal prisoners but objected to it for other groups, acknowledged that "problems . . . . have been raised by all thoughtful people" about the proposal to test immigrants. But he said that, as head of the Public Health Service, he had "no choice" but to designate HIV infection as a dangerous contagious disease.

Koop said the law required the Public Health Service to specify such diseases, but left immigration authorities "some leeway" in deciding what medical examinations to require of immigrants.

Dr. James Mason, director of the CDC, said strategies for implementing the new policy would be worked out by a task force including representatives of the State and Justice departments and the CDC.