T. LOUIS, Nov. 2 — Six student volunteers became the first people to receive smallpox vaccine here today as part of a study to determine whether existing stockpiles of the vaccine can be stretched to protect more Americans from bioterrorism.

"I thought this is an amazing opportunity," said Alison Hayes, a law student at Saint Louis University. "I can be vaccinated for my own protection and have the chance to help others should there be a smallpox outbreak."

Ms. Hayes, 26, of University City, a St. Louis suburb, is part of a study at the Center for Vaccine Development at Saint Louis University School of Medicine. In two to three months, 171 people, ages ´o 32, will receive varying strengths of the vaccine.

Smallpox, a highly contagious viral disease, was eliminated in 1980, but some terrorism experts fear that terrorists may have stockpiles.

In the United States, routine vaccination against smallpox ended in the 1970's. The government is making plans to produce enough new vaccine to immunize all Americans.

Meanwhile, the government wants to see if the existing 15 million doses of the vaccine could be diluted to deal with an outbreak. The National Institutes of Health is financing the study here and at three other locations.

Dr. Sharon E. Frey, an associate professor and the lead investigator in the Saint Louis University study, will inject volunteers with vaccine at full, one-fifth or one-tenth strength.

A similar study of 60 volunteers last year showed that 95 percent of those given full-strength vaccine were effectively immunized, compared with 70 percent of those given the one-fifth dilution. "The results with the one-to-ten solution were disappointing," Dr. Frey said.