tephen G. Sudovar, the president and chief executive of EluSys, a fledgling biotechnology company in Pine Brook, N.J., has what he thinks is an immensely promising anthrax drug, which might save patients' lives by inactivating deadly bacterial toxins.

But in dealing with the federal government, Mr. Sudovar, like others in his field, says he that has butted up against regulatory obstacles and research bottlenecks that may significantly delay the development of drugs to fight anthrax and other bioterrorism agents, just when there is heightened interest in such treatments.

Mr. Sudovar needs to test his drug in monkeys, and one of the few places in the United States that can do those tests is the Army Medical Research Institute of Infectious Diseases, in Fort Detrick, Md..

Mr. Sudovar said his monkey tests at Fort Detrick were supposed to begin in June 2002. But that was before the anthrax attacks. Now, all bets are off.

Fort Detrick's scientists are overwhelmed by requests from the Federal Bureau of Investigation for testing for anthrax spores, said Chuck Dasey, a spokesman there, and have had to delay animal tests of drugs or vaccines indefinitely. Companies like EluSys have to wait in an increasingly long line.

And that, medical experts say, is just one of the frustrating problems they face as they cope with a newly urgent problem of finding drugs to treat diseases that may be spread by bioterrorists. Another problem is figuring out what evidence the Food and Drug Administration will require to approve the drugs. A third, which arose with anthrax, is the issue of whether to try treating anthrax with drugs that look promising but that have been studied or approved only for other diseases.

F.D.A. regulations are a real problem, said Dr. Frank Young, a member of the board of EluSys and a former commissioner of the drug agency. Human testing to show effectiveness is required for all drugs. But it would be unethical to give healthy volunteers anthrax in order to test a drug. And anthrax has been too rare for tests on people who got the disease naturally. So, in 1999, the F.D.A. solicited comments on a new rule that would accept animal studies as proof of a drug's effectiveness against bioterrorism agents. But the rule has not yet been made final.

"The comment period is closed, but it's just wallowing in the agency," Dr. Young said. "It's a barrier to everything, including the smallpox vaccine. Without that rule being promulgated, it makes it very difficult to go forward with confidence that the agency will approve your drug."

Dr. Andrea Myerhoff, director of bioterrorism programs at the drug agency, said the rule was "in the process of finalization" and should be final in a few months.

Of course, the animal tests and the new regulation will not help in the awful event that more people develop inhalation anthrax in the coming months, medical experts say. But what about trying drugs already on the market?

Dr. Gerald Weissman of New York University School of Medicine notes that some drugs, including the high blood pressure drug captopril and the experimental rheumatoid arthritis drug anakinra, can block the anthrax toxin in the laboratory. Faced with an often lethal disease like inhalation anthrax, why not give the drugs to patients, he and others ask? The problem is that if drugs are given in an emergency, it can be impossible to know whether they helped or hurt.

For example, if an anthrax patient who was given captopril died of shock, it could be that captopril hastened death, or even caused it by lowering blood pressure. Or it could be that captopril and antibiotics were simply inadequate and the anthrax toxins killed the patient.

But, said Dr. Jonathan Moreno, an ethicist at the University of Virginia, he can understand why doctors may want to give anthrax patients approved drugs like captopril and or ask for emergency supplies of experimental drugs like anakinra, for this unapproved and untested use.

"It's a very tough call," Dr. Moreno said.

In the meantime, scientists who simply want to know if their experimental drugs work in animals say they are facing endless frustration.

Dr. John Collier at Harvard Medical School, for example, has found two promising drugs that may block the deadly toxin released by anthrax bacteria. But scientists at Fort Detrick can give him no date when they may be able test them in animals, even rodents.

Mr. Dasey, the spokesman at Fort Detrick, says his phone rings all day with calls from scientists wanting his help. He also gets e-mail messages, and letters. And many scientists call everyone they can find at Fort Detrick, all at once, Mr. Dasey said.

He tells the scientists that they can send in a proposal and wait to hear if the scientists at Fort Detrick are interested. Before the anthrax bioterrorism, it took a couple of months to get a reply, Mr. Dasey said. "There's no way to say how long it will take now," he added.

Mr. Sudovar says he is looking at other options, noting that there are a couple of other places that may be able to test his anthrax drug. But they, too, are overwhelmed with calls from scientists and companies seeking help.

Katy Delaney, a spokeswoman for the Battelle Memorial Institute, with headquarters in Columbus, Ohio, said her company did most of its research under contract for the Defense Department and preferred not to discuss its work. But she conceded that she had gotten quite a few calls from scientists and fledgling companies wanting to test drugs. Battelle, however, also is limited in what it can take on. "We were already busy before this started," Ms. Delaney said.