Scientists will begin testing in January whether they can stretch the nation's limited supply of an experimental bird-flu vaccine by pairing it with an immune-system booster.

Preliminary research with a different vaccine suggests that approach may work, Dr. Anthony Fauci, the National Institutes of Health's infectious disease chief, told a Senate panel Wednesday.

Senate Majority Leader Bill Frist, R-Tenn., also said lawmakers should pass legislation by Thanksgiving to fund the nation's preparations for a possible worldwide outbreak of bird flu or some other super-influenza strain.

That timetable has important implications: President Bush has proposed stockpiling enough of the anti-flu drugs Tamiflu and Relenza for 81 million people. The nation has only enough doses for 4.3 million people in stock and can't order more until Congress approves the money for it, said Dr. Julie Gerberding, director of the Centers for Disease Control and Prevention.

"We need it now," she told a hearing of the Senate Foreign Relations Committee.

On the vaccine front, U.S. health officials already have hired two companies, Sanofi-Aventis and Chiron Corp., to produce $162.5 million worth of vaccine against the virulent H5N1 bird flu, the strain that has killed at least 63 people in Southeast Asia since 2003. The U.S. government hopes eventually to stockpile enough H5N1 vaccine for 20 million people.

But a major barrier is that it requires two huge doses of the H5N1 vaccine to produce a protective immune response.

Chiron recently paired an experimental vaccine against another bird-flu strain, H9N2, with an immune-boosting chemical called an adjuvant. Preliminary testing, funded by NIH, in 96 people showed that adding the adjuvant dramatically lowered the required vaccine dose, results that Fauci called encouraging.

The next step is to test whether adding the adjuvant to the H5N1 vaccine will lower its required dose, he said.