The manufacturer of AZT, the only drug that has been approved as a treatment for AIDS, said yesterday it would cut the costly drug's price by 20 percent immediately.

Burroughs Wellcome Co. currently charges pharmacies about $8,000 for a year's worth of AZT, but patients often pay as much as $12,000 each. The company has been heavily criticized for making AZT one of the most expensive drugs ever sold, although Burroughs Wellcome officials say its development costs were unusually large.

"The inability of many people to afford to pay for this drug makes me very sad," said Dr. Samuel Broder, the National Cancer Institute researcher who helped develop the drug. "I'm not sure they needed to recoup all their costs in a year. They should have had the same faith in the drug that those of us who developed it have."

Almost 20,000 people in 37 countries are taking AZT, most of them in the United States. Although almost half of those who take it experience damaging side effects such as severe anemia, the drug has prolonged the life of thousands of patients who have had no alternative drug.

Currently, the drug is being tested on healthy people who have been infected with the HIV virus that causes acquired immune deficiency syndrome. The U.S. Public Health Service has estimated that up to 1.5 million Americans have been infected. If AZT proves beneficial to healthy carriers, Burroughs will have a huge new market.

Although the company will not release details of earnings and expenditures relating to AZT, it said yesterday it had sold more than $25 million worth between its approval in March and the end of August.

The company said yesterday that it would drop its wholesale price from $188 per bottle of 100 capsules to $150. At that price, a patient would spend about $22 a day for the recommended dosage. A spokeswoman said the decision came because the company is now capable of producing large quantities of AZT at lower costs.

"We have reached a point where we have achieved cost savings in production and we are passing them along to the consumer," said Kathy S. Bartlett, a company official. "We have always been aware of the impact AIDS has had financially and medically and we have tried to help."

AZT raced through the normally cumbersome federal approval process in record time. Twenty-two months from the day the first human received a test dose, the Food and Drug Administration approved it for widespread use.

Burroughs has repeatedly defended the price, saying it took a major financial risk to develop AZT. In congressional testimony earlier this year, officials said the company had committed $80 million to producing the drug.

But for many poor AIDS patients with little or no health insurance, the $12,000 annual price tag has been overwhelming. Even patients whose private insurance pays 80 percent of the costs can pay up to $200 each month out of their own pockets.

"I'm delighted to see this move by the company," said Rep. Henry A. Waxman (D-Calif.), whose subcommittee held hearings on the price and availability of AZT earlier this year. "But we don't know on what basis they set their original price, so we don't know how they arrived at the new rate. I'm afraid many people are still going to have a hard time getting access to this drug."

While many public health officials involved in treating AIDS patients were surprised by the high price, others said that without the incentive of large potential profits, no company would ever attempt to develop such a drug.

"The company was a pioneer," said Dr. Michael Gottlieb, a Los Angeles physician who was one of the first in this country to treat AIDS patients. "They scored a big win in a risky business. We can't penalize them for being willing to take a chance when nobody else would."

Company officials have long feared that their product would quickly be eclipsed in the marketplace by a newer and better generation of AIDS drugs. It has become clear over the last six months, however, that AZT will remain at least a central -- and possibly the only -- approved treatment for the forseeable future.

While several major drug tests are under way with other chemical agents, none of them has progressed far enough to be approved. In addition, the most promising among them, DDC, which is a chemical cousin of AZT, produced unexpected problems when it was given to humans in large doses.

Before the AIDS virus can multiply it needs thymine, one of the four building blocks of DNA. AZT, or azidothymidine, mimics the structure of thymine and attaches itself to the viral DNA chain, ending it prematurely. As a result, the virus can no longer multiply.

"It's the one drug in the game right now, so of course this is a step in the right direction," said Jeffrey Levi, executive director of the National Gay Rights Task Force. "But the drug remains out of the reach of many people. Burroughs has a monopoly and they still have not justified their pricing structure. We can only hope this {price-cutting} trend will continue."