About 4 percent of American cases so far have been attributed to infections acquired in heterosexual intercourse.

As Burroughs Wellcome increases AZT production, the drug will be more widely available, company officials said. Since no other drug has been approved by the Federal Government for treatment of AIDS and related conditions, it is widely expected that most patients will insist that their doctors prescribe it for them. More than half the approximately 14,000 surviving AIDS patients have had Pneumocystis carinii pneumonia, or PCP, placing them in one of the priority categories for receiving the drug.

In announcing approval of AZT by the F.D.A., Dr. Robert E. Windom, an Assistant Secretary of Health and Human Services, said:

''Today's approval marks an important step, but by no means a final victory, in our ongoing war against AIDS. Retrovir is not a cure for AIDS, but it has a demonstrated ability to improve the short-term survival of AIDS patients with recently diagnosed PCP and certain patients with advanced ARC.''

About 33,000 cases of AIDS have been reported to the Federal Government since 1981 when the disease was first detected. More than half have resulted in death. In addition, the Public Health Service estimated that two to three times as many Americans suffer from advanced symptoms of AIDS-related complex, which often progresses to AIDS. Federal officials project the number of cases of AIDS will rise rapidly, reaching 270,000 by the end of 1991. $8,000 to $10,000 a Year The cost of AZT - $8,000 to $10,000 a year - has been seen by some promoters of homosexual rights as a drawback.

The Gay Men's Health Crisis, a voluntary organization in New York that assists AIDS victims, said it was pleased by the licensing of AZT but concerned about the price.

''This licensing represents another step forward in the research on AIDS,'' the group said. ''We are, however, outraged at the extreme high cost of the drug and the fact that a person with AIDS may be forced to spend down all their assets in order to afford this excellent drug.''

Lori Behrman, the spokeswoman for the group, said the Government and the drug industry ought to set aside money to help pay for the drug for those who who cannot afford the full cost since, if paying for the drug forced them onto welfare, it would cost society more in the long run.