More than 71,000 cases of AIDS have been reported worldwide by 129 countries, but because of incomplete surveillance and reporting, the true case count is probably closer to 150,000, according to a new report from the World Health Organization.

Another 150,000 cases are expected during 1988, bringing the disease's estimated worldwide toll to 300,000 by the end of next year, said Dr. James Chin, chief of surveillance, forecasting and impact assessment at WHO's Special Programme on AIDS.

In the last year, the willingness of public officials to acknowledge the presence of AIDS in their countries and report cases to WHO has increased dramatically, Chin said. Over three-quarters of the world's countries have now reported cases, and about 160 have agreed to participate in the organization's case-tallying effort. A year ago, only about 80 countries were reporting the disease.

Before confronting AIDS as a public health problem, "most countries will have a denial phase," he said. "(The year) 1987 was a period when many countries went into the next phase, abandoning the denial and beginning to pay more attention to what was going on."

The United States has by far the largest number of reported AIDS cases, with 49,342 as of yesterday, according to the federal Centers for Disease Control. Cases recorded by WHO through Dec. 2 show France as second, with 2,523. The other countries with more than 1,000 reported cases are, in order of rank, Uganda, Brazil, Tanzania, West Germany, Canada, the United Kingdom, and Italy.

Chin said the completeness of AIDS reporting varies greatly among different countries. He estimated that in the United States, which has the most reliable surveillance, between 80 and 90 percent of AIDS cases are reported. In other industrialized countries, the majority of cases are reported, but in developing countries, "it is clear that the majority of cases have not been recognized or reported," he said.

He said the situation has improved gradually over the last year, with a number of countries starting to report cases officially and others increasing surveillance. For example, Zaire recently reported cases to WHO for the first time and Uganda has improved its case-finding system and has begun a blood-sampling survey to determine what proportion of its population is infected with the virus.

Chin said that in addition to changes in the political climate surrounding AIDS, the growth of the epidemic has made its existence harder for countries to ignore. "Some hospitals are bursting at the seams with cases," he said.

The organization estimates that between 5 and 10 million people are infected with the virus worldwide and that between 500,000 and 3 million new AIDS cases will occur over the next five years. The report said the virus has probably spread to every country in the world.

The predominant patterns of infection differ from region to region, the report said. In North America, Europe, Australia and New Zealand, the majority of infections have occurred among homosexual or bisexual men and intravenous drug abusers.

In Africa and Haiti, the major mode of spread is heterosexual intercourse, with many infections also occurring via transfusions, through the use of nonsterile needles in health care settings, and through transmission from infected mothers to their infants.

In Asia, where the AIDS virus is still relatively rare, most infections have occurred in individuals exposed to blood or blood products imported from countries with higher AIDS rates or in those who had sexual contact with people from such countries, the report said.

In an accompanying policy statement on international AIDS control, the WHO condemned the use of quarantine or other forms of discrimination against those infected with the virus. It endorsed the need for informed consent for testing, counselling and guaranteed confidentiality in programs to test individuals for exposure to the virus.