QUITO, ECUADOR -- From Mexico to Argentina, the rate of new cases of acquired immune deficiency syndrome is increasing rapidly, and many health officials now fear that Latin America will probably become the next battleground against this lethal disease.

"It is a problem that is facing all of the countries of the Americas," said Dr. Fernando Zacarias, regional adviser on AIDS for the Pan-American Health Organization.

Speaking here at the first international meeting on AIDS in Latin America, Zacarias pointed out that more than 9,000 cases have been reported so far in the region's 44 countries. As much as 2 to 3 percent of the population in some areas of the Caribbean may be infected with the AIDS virus.

"This is a very rapid and dramatic increase in AIDS," he said.

The World Health Organization estimates that 5 to 10 million people throughout the world already are exposed to AIDS, and experts believe that most will eventually develop symptoms of the disease. More than 45,000 of the world's 60,000 cases have been reported in this hemisphere -- the bulk of them from the United States. But now the disease in such countries as Mexico and Brazil is starting to catch up.

"One of the big concerns is that the virus is introduced into countries in a way similar to Africa," said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases. "Public health officials fear that they may see an explosion of cases as they have seen in Africa."

Without a drug to cure those infected or a vaccine to block the virus, information about how to prevent the spread of the virus remains the most powerful weapon available to physicians.

To help plan prevention strategies, more than 500 AIDS experts and public health officials have gathered here for a two-day teleconference. Through satellite links, the conference is being beamed to an estimated 60,000 doctors, nurses and other medical workers at 500 sites in 30 Latin American countries, including Cuba.

Experts in Quito point out that fighting the spread of AIDS poses special problems in Latin America. Screening blood donations, for example, still is not performed in many countries because of the relatively high cost of the test to detect antibodies to the virus in blood samples. In Brazil, donated blood comes from private laboratories and only recently were these facilities required to test for the AIDS virus.

In other countries, the tests are simply too expensive. "We do know that in some countries, almost 2 percent of blood donors have antibodies to the AIDS virus," Zacarias said.

AIDS prevention is also complicated by the fact that among the countries of the Americas, there are four main languages: Spanish, Portuguese, French and English. In addition, most countries report high rates of poverty so that many people are not able to get effective medical care.

Throughout the first day of the conference, participants in distant cities posed questions via satellite to the panel of experts in Quito.

One issue that surfaced was whether women who were infected with the virus continue breastfeeding their babies. Mann reported that the W.H.O. had concluded that the benefits of breastfeeding still outweigh the risks of infecting the babies through the breast milk. However, if adequate alternatives to breastfeeding exist -- as they do in the United States, health officials recommend that mothers stop breastfeeding.

Another recurring question involved the risk of spreading AIDS by bedbugs and mosquitos.

All the experts agreed that mosquitos and other insects could not transmit the AIDS virus, and many argued that the 'mosquito question' was getting too much attention. The virus is spread mainly through intimate sexual contact and exposure to contaminated blood. As Dr. Jonathan Mann, director of the W.H.O.'s program on AIDS, said: "It is not whether you put up a mosquito net but what you do under it."

Within Latin America, there are wide differences in how the disease is spreading.

In Costa Rica, for example, only one woman is known to have contracted AIDS. The disease is largely confined to homosexuals and to hemophiliacs who were infected by contaminated blood transfusions.

In Haiti, however, the pattern is different. In 1983, when the first AIDS studies were performed in that country, 65 percent of the male AIDS patients were homosexual or bisexual. Only 10 percent of the total cases were female. A year later, the disease was spreading heterosexually. By 1986, 38 percent of the AIDS cases in Haiti were heterosexual women.

"Our population is essentially bisexual with more contact with women than men," said Dr. Jean Pape, director of the Haiti AIDS program. "Many more prostitutes carry the disease."

So far, Haiti has reported 851 cases, though health officials believe the toll exceeds 1,000.

In some Caribbean countries, said Zacarias of the Pan American Health Organization, 3 to 9 percent of the pregnant women carry the AIDS virus and are likely to pass it on to their unborn babies.

Many public health officials are looking to other countries to see what lessons can be learned that may help predict the course of the disease in the U.S.

Fauci of the National Institute of Allergy and Infectious Diseases cautioned against forecasting a dramatic rise in heterosexual cases in the U.S. based on the Haiti experience. "Haiti has many characteristics that are similar to Central Africa," he said. These include a higher incidence of other sexually transmitted diseases such as syphilis and gonorrhea, which may increase the chances that the AIDS virus can be transmitted heterosexually.

Brazil -- with 1,695 reported cases as of April 30 -- now has more cases than any African country. In addition to the U.S., only France has a higher incidence with more than 2,000 reported cases as of June 30.

In Brazil, the disease appears to be most prevalent among homosexuals, especially around Rio de Janeiro. As in the U.S., said Fauci, intravenous drug use also seems to play a role.

Only four of the 45 countries making up the Americas have reported no AIDS cases according to W.H.O. officials. Even Cuba has admitted to three cases as of December 1986. And it's not just the increasing toll of AIDS that has officials worried but the the number of cases for the size of the country. On island countries of Trinidad and Tobago with 1.1 million people, there are already more than 200 cases as of March 31.

AIDS is also emerging as a major problem in Mexico. Although the true extent of the spread of the disease is not yet known, "it is growing," said Dr. Jaime Sepulveda, director general of epidemiology in the Mexican Ministry of Health and president of the Mexican National AIDS committee.

More than 700 AIDS cases have already been reported, making Mexico the fifth highest of the Americas in AIDS cases.

As in all countries, the number of cases only hint at the number of people already infected with the AIDS virus. To see how far the infection has spread, Mexico has conducted a household survey that has tested the blood of some 70,000 of the nation's 80 million residents.

A representative sample from all socioeconomic groups in both urban and rural areas have been tested, Sepulveda said, so that the study will give a good indication of the virus's spread.

Results of the study are not expected to be available until next June, when the third international AIDS conference meets in Stockholm.

The largest number of AIDS cases is in Mexico City, primarily because it has a large homosexual community. Guadalajara and the areas along the border with the U.S. also have high AIDS rates. Sepulveda said that it's not clear whether Mexicans returning from the U.S. are bringing the disease back to Mexico.