mid concerns that Middle Eastern terrorists might have procured radioactive weapons, the Defense Department is pressing for approval of a novel drug that could help protect people from radiation.

As fears of terrorism grow, the drug, known as 5-androstenediol, is receiving increased scrutiny along with other experimental treatments and drugs already on the market. The National Cancer Institute, the Department of Defense and the Department of Energy have invited leading radiation experts to a workshop in Bethesda, Md., on Dec. 17 and 18 to review approaches for protecting people from radiation.

The drug is a steroid hormone that appears to strengthen the immune system. It was developed by Dr. Roger M. Loria, a professor at Virginia Commonwealth University, and rights to it are held by Hollis-Eden Pharmaceuticals (news/quote) of San Diego.

"This is an area that hasn't gotten a whole lot of attention," said Dr. John E. Moulder, professor of radiation oncology at the Medical College of Wisconsin. "Working on trying to cure patients of cancer gets you more headlines than working on treating people for nuclear accidents that you hope will never occur."

So far, the Hollis-Eden drug has been tested as a radiation protectant only in mice. In one test, an injection protected 70 percent of mice from a level of radiation that killed all the mice in the control group.

Dr. Thomas M. Seed, leader for radiation casualty management at the Armed Forces Radiobiology Research Institute in Bethesda, said the drug was his institute's leading candidate for something to give to soldiers in advance of possible radiation exposure. Such a drug would also be useful for civilians, including people responding to an accident at a nuclear power plant, he said.

Since it would be unethical to expose people to large doses of radiation to test the drug's effectiveness, Dr. Seed said he hoped the Food and Drug Administration would approve it under a new rule allowing tests on monkeys or other animals.

American officials have said there is little evidence that Osama bin Laden has obtained nuclear weapons. But some experts have said terrorists might try to make a so-called radiological bomb by combining conventional explosives with radioactive material like spent nuclear fuel.

Hollis-Eden has been testing a drug similar to androstenediol as a treatment for AIDS, the idea being to stimulate the patient's own immune system to fight the virus.

For defense use, the drug is aimed mainly at preventing death from intense radiation in the short term by restoring various kinds of infection- fighting immune system cells. Radiation can kill the immune system, leaving victims vulnerable to potentially fatal infections.

Some radiation experts were cautious, saying the Pentagon, hoping to have soldiers function in a nuclear war, had tried many such compounds without success. In some cases the protection afforded was not enough, and some drugs seemed to protect animals but caused bad side effects in people.

The Hollis-Eden drug could have other problems, too. It needs to be injected, which can take time in an emergency. And it would probably not be possible to know of exposure in advance of a terrorist attack.

In addition, Dr. Fred Mettler, chairman of radiology at the University of New Mexico, said that just solving the immune system problems might not be enough because people could still die months later from other types of radiation-induced damage, such as to the lungs.

Dr. David J. Grdina, professor of radiation oncology at the University of Chicago, said it was more important to develop drugs that protect people against cancer from radiation than against the immediate lethal effects. More people are likely to be exposed to sublethal doses of radiation while cleaning up or standing guard at the site of a radioactive attack than might be exposed to lethal doses in the attack itself, he said.

The Nuclear Regulatory Commission is moving toward stockpiling millions of potassium iodide pills to prevent thyroid cancer in those exposed to radioactive iodide if a nuclear power plant was attacked.

Dr. Grdina is trying to use a drug called amifostine to prevent cancer from radiation. The drug, sold as Ethyol by MedImmune Inc. (news/quote) of Gaithersburg, Md., is already approved to protect the salivary glands from radiation therapy used to treat head and neck cancer.

Dr. Moulder has found that two drugs for high blood pressure, ACE (news/quote) inhibitors and A2 blockers, protect animals from the kidney failure and lung damage that can occur months after radiation.