WASHINGTON -- Three-fifths of Americans say they would want a smallpox vaccination if it were widely available, according to an Associated Press poll that suggests continued nervousness about bioterrorism.

About half of the respondents say they are concerned about the threat of a smallpox attack and think last month's anthrax attacks are the beginning of an extended campaign, according to the poll conducted for The AP by ICR of Media, Pa.

Some of those still concerned about bioterrorism say they generally are nervous because they do not know what's coming next.

"To me, now, anything can happen," said Michelle Hunt, a 50-year-old retail clerk from Boulder City, Nev. "If it's out there, it could happen. I try not to worry about it."

The U.S. government is stockpiling the smallpox vaccine in case of terrorist attacks, but has no plans to routinely vaccinate the general public. Smallpox vaccine is made with a live virus related to smallpox, so it can cause some very serious side effects. Experts estimate that if every American were vaccinated against smallpox, about 400 people would die from the vaccine.

A majority of Americans indicate that they would get the vaccine if it were available, even after they are informed of the possible risks.

"Smallpox is incredibly contagious, and they only have 15 million vaccinations," said 28-year-old Bradford Rubinoff of Tucson, Ariz. "If people would use anthrax against us, who's to say they wouldn't use smallpox?"

Asked if he would want to get the smallpox vaccination even though it carries some health risks, Rubinoff said, "Absolutely."

Among the risks: About three in every 1 million people vaccinated would get encephalitis, which can cause permanent brain damage or death. Another 250 would get a smallpox-like rash that also can be fatal if not properly treated.

People with weak immune systems -- patients who have AIDS, cancer or organ transplants or who are taking high-dose steroids -- are most at risk for the side effects, as are people with the skin condition eczema.

The anthrax attacks through the mail, which rattled the nation throughout October, had begun to subside a bit.

But last week's discovery of a suspicious letter to Sen. Patrick Leahy, D-Vt., may revive public concern.

People are evenly split about whether the anthrax attacks are part of a long-term campaign.

The number who think the anthrax attacks are likely to continue in the coming months is 45 percent, down only slightly from the height of the anthrax scare in mid-October, according to the poll of 1,003 people taken Nov. 9-13. The poll, conducted before the discovery of the Leahy letter, has a margin of sampling error of plus or minus 3 percentage points.

Young adults between 18 and 34 were twice as likely as those over 65 to think the anthrax attacks are the beginning of a long terror campaign.

"I am worried about it," said 18-year-old Veronica Gallo of San Bernardino, Calif. "Watching it on the news over and over -- it scares me. I tend to stay more with my family these days. It's pretty much all the stuff that's going on ... anthrax, plane crashes."

Some of the continuing concerns about anthrax may have to do with bad information. A quarter of the people in the poll erroneously think anthrax is contagious.

About a fourth of the public say the handling of the anthrax scare gave them more confidence in the government's ability to protect citizens from future terrorist attacks.

Almost that many say it gave them less confidence -- with Democrats twice as likely as Republicans to say they had lost confidence. About half said it has not affected their confidence level.

"My confidence was not affected," said 26-year-old Christine Jarrell Ratke, a college student from Ferndale, Mich., near Detroit. "I was not surprised they were slow to react. ... It's new, and the government isn't perfect. I don't think it can protect us from everything."