LONDON, JAN. 26 -- Delegations from more than 150 countries, including 121 ministers of health, gathered here today for the first worldwide governmental meeting on Acquired Immune Deficiency Syndrome, or AIDS.

Jointly sponsored by the World Health Organization (WHO) and the British government, the three-day gathering is designed for governments to share information about how the disease has spread in each of their countries, and about the nationwide educational and public health programs they have developed to curtail it.

The gathering marks the first time the AIDS epidemic has been substantively addressed worldwide as a political problem, rather than on a scientific or medical basis.

Its organizers stressed that, in the absence of an AIDS vaccine or cure, information and health programs are the only proven way of stemming the spread of the disease. They hope that by exposing delegates to the way others are handling the same crisis, more public health officials will be able to marshall the political will, and the informational skills, to make their own programs more effective.

"The successes and failures of one country are relevant in others," said Dr. Jonathan Mann, director of WHO's special program on AIDS. "One should never underestimate the value of seeing how someone else has done something you're not quite sure how to do. There is strength from common purpose."

In his opening speech, Mann described the "economic, social, cultural and political reaction" to AIDS as a "third epidemic," along with infection from the virus and actual development of the disease.

Outlining the latest figures on the global scope of AIDS, Mann said a total of 75,392 cases, in more than 130 countries on all continents, had been reported to WHO in the nearly 10 years since reporting began. Seventy-five percent of the cases had come from 42 countries in the Americas, 12 percent from 27 European countries, 12 percent from 38 African countries, and the remaining 1 percent from Asia and Oceania.

According to WHO statistics, nearly two-thirds of the reported cases, almost 50,000, had been reported in the United States. But Mann and others emphasized that reporting procedures in some countries had likely skewed the figures. Mann said that WHO estimated the true number of cases worldwide at about 150,000.

The number of new AIDS cases expected in 1988, he said, is expected to equal that 10-year total.

The political pitfalls of involvement in such a delicate issue as AIDS education -- and what WHO officials called the "sensitive and secret" forms of human behavior through which it spreads -- quickly became apparent at today's session.

In a speech officially opening the conference, Britain's Princess Anne departed from her prepared text, already distributed by WHO, to describe the disease as "a classic 'own goal' scored by the human race on itself; a self-inflicted wound that only serves to remind Homo sapiens of his fallibility."

She went on to describe "the real tragedy" of AIDS as the "innocent victims, people who may have been infected unknowingly, as the result of a blood transfusion, and the few who may have been infected knowingly by sufferers seeking revenge, but possibly worst of all by those babies who are infected in the womb and are born with the virus."

Princess Anne's remarks brought an immediate response from the Terrence Higgins Trust, Britain's leading nongovernmental AIDS educational and counseling agency, which said it was "appalled that she make judgment on how people who are affected . . . became infected."

Trust spokesman Nick Partridge said that "by saying that some people are innocent, it implies that some are guilty . . . It's a line of argument we thought had been put to rest many years ago."

Differences in the methods of educating populations about AIDS were evidenced by a conference hall exhibition in which a number of governments displayed educational posters and pamphlets distributed in their countries.

To a large extent, variations in theme depended upon the most prevalent regional method by which the disease is spread. In African countries where AIDS is spread primarily through heterosexual intercourse, materials tended to stress the importance of marital fidelity and adherence to religious beliefs.

In the Scandinavian exhibits, safety in homosexual sex was emphasized. A variety of British television advertisements and posters stressed the dangers of intravenous drug use.

Among the scantiest exhibits was that of the United States, which is among a relative handful of the world's countries that has not adopted a nationwide, government-sponsored education program.

The United States also was one of the few governments not represented by its health minister, although Assistant Health Secretary Robert E. Windom was accompanied to the meeting by U.S. Surgeon General C. Everett Koop and governmental AIDS coordinator Peter Fischinger.

{A spokesman for Health Secretary Otis R. Bowen said the secretary did not attend the conference because of the State of the Union address Monday night by President Reagan. "He had to be present," said spokesman Chuck Kline.}