WASHINGTON - Federal scientists are preparing the first studies of U.S. SARS patients to figure out how long they're contagious and to see if experimental treatments might help.

The National Institutes of Health will soon offer some of the 52 people in the United States considered probably infected the option of coming to its acclaimed Bethesda, Md., hospital for the research.

"There's an awful lot we don't understand about the pathogenesis of the disease" that requires research in a specialized center, said Dr. Anthony Fauci, director of NIH's National Institute for Allergy and Infectious Diseases.

The government is stockpiling ventilators, training health workers and encouraging hospitals to create isolation wards in case the SARS virus spreads here the way it has in China, Canada and elsewhere.

Some of these efforts were under way as part of the government's attempt to prepare for a possible bioterrorism attack, while others are a reaction to the global spread of severe acute respiratory syndrome.

So far, the country has done a good job preventing the spread of SARS here, but many local officials would not be prepared if the virus took off in their communities, top officials at the Department of Health and Human Services said Wednesday.

"I don't think there is any country, including our own, that is right now capable of massive infusion of individuals who are severely ill, requiring intensive care under isolation," said Fauci.

Worldwide, there have been more than 5,400 cases of the highly contagious respiratory disease, with at least 375 deaths. Besides the 52 probable U.S. cases, more than 200 other cases here are considered suspicious. No one in the United States has died from SARS.

No one knows why. Scientists haven't yet found any medications that effectively treat SARS, and supportive care is no better here than in Canada, where 21 people have died.

Key to fighting SARS is preventing its spread, yet no one even knows exactly when people are contagious. The NIH has made a priority of studying people who are recovering to find out when they quit transmitting the virus.

Fauci also hopes to try a different approach at treatment - working with patients' immune systems to spur recovery.

One option is to cull an immune system cell called immune globulin from the blood of recovering patients. Injecting that substance into the very sick has worked for certain other diseases, and if animal tests proved promising, scientists could try it with SARS.

The plans sparked some protest among NIH employees about bringing SARS patients to a hospital that routinely houses cancer patients and others with very weak immune systems. But Fauci said that immune-weakened patients are in every hospital that will have to treat SARS - and that NIH's hospital is upgrading its already strict isolation ward to guard against spread of the virus.

Research aside, HHS officials stressed Wednesday that the country must be ready if SARS suddenly spreads here like it did in Toronto.

To help, HHS is buying 3,000 ventilators to supplement those now available in the national stockpile. About 100,000 ventilators are operating in the country, with about 80 percent usually in use, and many as 95 to 100 percent taken during the flu season.

HHS Secretary Tommy Thompson would not say how many ventilators are now in the stockpile but said the additional 3,000 was a big increase.

Many communities do not have enough beds to house a large number of sick people with contagious diseases. By the end of the year, every region is supposed to have beds to house an unexpected surge of 1,000 infectious patients; federal funding for bioterrorism preparedness is helping.

And Dr. Julie Gerberding, director of the Centers for Disease Control and Prevention, meets with Canadian officials Thursday to learn how they were able to contain the virus.

Gerberding said Canadians have taken steps that go beyond what U.S. hospitals are used to in handling infectious diseases: transferring patients from one hospital to another, closing some hospitals, canceling elective surgeries and furloughing health care workers who were exposed to SARS patients.

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On the Net:

SARS information: http://www.cdc.gov/ncidod/sars/

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Associated Press Writer Laura Meckler contributed to this report.