The government has launched a broad effort to develop vaccines and drugs against the SARS virus, an attempt to be prepared if the disease now causing panic and social unrest in China turns into a worldwide pandemic that threatens the United States.

Top government scientists said they are moving rapidly on multiple fronts to jump-start treatment and prevention research, particularly on vaccines. Experience with related diseases in domestic animals suggests a vaccine against severe acute respiratory syndrome may be possible, and scientists outside the government said that strong federal leadership could conceivably produce one in as little as a year, although two to three years is more likely.

These efforts by the National Institutes of Health come as many private companies have been hesitant to invest in SARS research, not certain whether the disease will be a lasting phenomenon. The NIH is rapidly negotiating agreements and awarding grants to propel research in public and private laboratories around the nation.

"Quite frankly, I don't think SARS is going to fizzle out," said Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, a unit of the NIH. "This is a really unusual situation where you are in the midst of the evolution" of a new disease, he said. "You have to make strategic decisions about public-health measures now."

Scientific theory suggests not only that a vaccine is possible to ward off the disease but also that various kinds of treatments might be developed to aid people after they are infected. The goal would be to lower the SARS death rate of about 6 percent, which scientists consider alarmingly high for an ailment that may spread almost as readily as the common cold. The government expects to push drug approaches that have proved useful in treating other respiratory ailments and in combating AIDS.

The immediate focus is on vaccines that could be used to prevent new infections in regions experiencing a SARS outbreak. Various government laboratories, enlisting the aid of private companies, are pursuing at least four potential approaches to making a vaccine, including the two methods that Jonas Salk and Albert Sabin used half a century ago to develop vaccines against polio.

It's by no means certain that any approach will work, and the SARS virus, which belongs to a family of viruses that mutate rapidly, could outwit the best efforts of American science. The AIDS epidemic is a cautionary example: As research on that plague cranked up in the mid-1980s, scientists promised a vaccine within a year or two, but they have yet to produce one nearly 20 years later.

Still, theory suggests that SARS will be an easier problem to solve than AIDS. The human immune system is generally unable to contain a virus like AIDS, but it usually does so with SARS, after a period of severe illness. "When you have an infection in which the majority of the people, in fact the very large majority of the people, spontaneously recover, eliminating the virus from their body, that's a very big hint that you can get a vaccine," Fauci said.

In an interview, Fauci said his plan is to pursue all rational approaches to vaccines in simultaneous research programs, essentially setting up a race between various laboratories specializing in different techniques to see which can create something useful. Government scientists said Fauci has called people at the NIH into urgent sessions to lay down what amounts to a strategic plan for tackling SARS research as rapidly as possible. Congress has yet to appropriate money for such research, and indeed, nobody at the NIH is sure yet how much will be needed, particularly to lure private companies into the campaign.

"We're just going to do it, and we'll talk about the money later," Fauci said. "It's got to be done."

The government's plan is, in part, an attempt to take advantage of the extraordinary power of modern genetic science. Identifying the cause of AIDS took two years after serious research started. With SARS, scientists not only identified the new virus but also published a complete genetic map of that germ within weeks of the first awareness of the ailment in the West.

Despite that progress, and rapid work on a diagnostic test, the only available method to combat SARS is the crudest weapon in the public-health arsenal: quarantine. Vietnam appears to have had some success controlling SARS through quarantine alone, but the disease is spreading widely in China, and many experts fear an explosive outbreak as the weather turns colder this fall.

To develop new tools, the government wants to explore new vaccines. Vaccines are essentially a trick to teach the immune system how to attack an incoming germ before it can cause illness. One of the first approaches that scientists will employ is the one Salk used to produce his famous poliomyelitis vaccine in 1952. That is simply to grow cells in flasks, allow the virus to infect the cells and reproduce, and then kill the virus, most likely with a chemical called formalin. The virus would then be injected as a vaccine, and though dead, it might retain enough characteristics to elicit an immune response that would later be effective against live SARS.

But even if it works, this approach poses difficulties. Scientists would need to grow large amounts of a dangerous virus, creating tricky containment problems. The resulting vaccine also would have to be tested carefully for dangerous side effects. And making sure the virus is truly dead in every vaccine batch would be no small feat. Some recall a disaster in 1955, during the nationwide Salk vaccination campaign, when a batch containing live virus slipped through and the vaccine itself wound up causing polio.

A second vaccine approach involves deliberately using a live strain of the virus, but one so weakened that it is unlikely to cause disease. Sabin used this "attenuated" vaccine method to create his polio vaccine, which wound up being preferred to the Salk vaccine in many countries. Such a vaccine can generate a strong immune response, but it also poses risks. A chief one is that the weakened virus can mutate in a way that makes it virulent again, and the vaccine itself could set off an epidemic.

As these older methods go forward, scientists also plan to use some of the high-technology approaches in their arsenal to develop more modern vaccines. The NIH is putting high hopes in a method that involves inserting SARS genes into a mild germ called adenovirus. The resulting hybrid should be incapable of causing disease, but it will look enough like SARS to the immune system that it might elicit a strong response. The government just awarded more than $400,000 to GenVec Inc., a small biotechnology company in Gaithersburg, and signed two contracts to enlist the company's technology for this effort. "We're very impressed by what it does in animal models," said Gary Nabel, director of the NIH's Vaccine Research Center.

Yet another vaccine approach will involve using genetic engineering to make copies of a protein on the surface of the SARS virus. The protein will be given as a vaccine, in hopes the body will mount an immune response to the protein that would kick in again if SARS viruses bearing similar proteins came along later. One concern is that this approach was tried in animals with a virus related to SARS and it not only failed to prevent infection, but made the resulting disease worse.

Fauci and Nabel cautioned that this prospect, and other safety concerns, must be carefully ruled out in human safety testing for any vaccine the nation develops, a necessity that makes them reluctant to promise rapid progress. While some scientists in laboratories outside the government think a year or two is doable for a vaccine, many others are skeptical. "Vaccines are going to take years and years and years. And years," said Donna Ambrosino, director of Massachusetts Biologic Laboratories.

In addition to the four possible approaches to a vaccine, the government wants to explore whether new drugs can be created.

Ambrosino's outfit, a unit of the University of Massachusetts Medical School that develops drugs, favors an approach that could, in theory, lead to a rapid treatment for people already infected with the SARS virus. With government encouragement, she has signed an arrangement with Medarex Inc. of Princeton, N.J., to use genetic engineering to create artificial antibodies to SARS. Antibodies are proteins that the immune system uses to fight off a germ, and artificial ones could be given as a drug. This approach has worked well for a respiratory ailment in premature babies -- indeed, the resulting drug, called Synagis, is fast becoming a billion-dollar blockbuster for MedImmune Inc. of Gaithersburg.

Another treatment approach that could yield relatively rapid results is to screen compounds that drug companies have already developed to see if any are active against the SARS virus. The first AIDS drug, azidothymidine, or AZT, was found that way -- it was an old, failed cancer drug that was brought back to life in the 1980s when it turned out to suppress the human immunodeficiency virus, which causes AIDS. In recent weeks, companies have scoured their shelves and sent scores of compounds to the government for testing against SARS.

In the longer term, the government wants to study other methods that could be used to attack the SARS virus in infected patients. When it takes control of human cells and hijacks their genetic machinery to reproduce itself, the virus depends on a type of enzyme called a protease to do much of the construction work. HIV uses the same type of enzyme for the same purpose, and drug companies have had success designing protease inhibitors that help to block reproduction of the virus. HIV protease inhibitors are unlikely to work against SARS, so scientists will probably have to start from scratch to design new ones -- but the HIV experience has taught them how to do it.

Some laboratories plan to try even higher-tech methods. In what amounts to a Hail Mary pass to try to create a rapid and effective SARS drug, a company called AVI BioPharma Inc. of Portland, Ore., has designed a compound the company says may be capable of gumming up the virus's genetic machinery. Drugs like this are known as antisense compounds, and scientists have had big technical problems getting the approach to work, but Patrick Iversen, senior vice president of research and development at AVI, contends that his company has largely resolved them.

If by wild chance the AVI drug or another like it proves to work, the era of "Star Trek" medicine will have arrived, for antisense is a remarkably rapid approach. Yesterday, just 13 days after a newly recognized virus was proven to be the cause of SARS, AVI shipped a drug designed to block that specific virus to U.S. Army laboratories in Frederick for testing.