The Centers for Disease Control and Prevention began training state and local health officials Monday on how to recognize smallpox and quickly contain an outbreak spread by bioterrorists.

Arming about 200 public health workers with thick binders of information, the CDC began three days of classes on how the highly contagious and deadly virus might be spread.

"It's a sad day that we feel this meeting is necessary," said Dr. Walter Orenstein, chief of CDC's National Immunization Program. "I hope and pray that this is a big waste of time."

The CDC stressed it has no credible evidence that intentionally released smallpox is any more of a threat than it was before Sept. 11.

But the virus could be much more dangerous than anthrax if it were released by terrorists. It causes a pock-like rash all over the body, and can be spread through the air.

The CDC wants to make sure state and local health officers — the first line of defense against a bioterror attack — don't confuse smallpox in its early stages with less dangerous infections, like chickenpox or even syphilis.

It also wants those officials to be familiar with the CDC's emergency smallpox plan, released last month, which calls for immediate quarantine of a confirmed case and vaccination of people who came in contact with the infected person.

"We have a large, susceptible civilian population," Orenstein said. "The threat of smallpox is probably not zero, although it is close to zero, and given its severity we need to be better prepared."

Smallpox appears first as tiny bumps, sometimes too small to be noticed. The bumps gradually swell and become filled with pus, finally turning into contagious scabs that fall off the body.

Mass vaccination against smallpox ended in the United States in 1972, and the disease was declared eradicated 1980, with small stocks of virus kept at CDC's labs in Atlanta and at a lab in Russia.

Bioterrorism experts fear some of the Russian stockpile may have fallen into the hands of rogue scientists in other nations. Speakers at the CDC training meeting Monday listed Russia, Iraq and North Korea as possible smallpox sites.

CDC deputy director Dr. David Fleming urged the state and local officers to plan with their counterparts in law enforcement because an outbreak might require them to use unusual power to quarantine the public.

Law enforcement might also have to handle a rush for smallpox vaccine if a case is confirmed, Fleming said. Health officials are wary of vaccinating people unnecessarily because of hideous side effects, even death, caused by the vaccine in rare cases.

Smallpox vaccine is administered with a bifurcated needle, which has two tiny prongs at its tip. The government has about 1.2 million of the sterilized needles now and plans to boost the stockpile to 15 million by March, said the CDC's Dr. William Atkinson.

The Bush administration has said it will have enough vaccine on hand by next year to inoculate every American against smallpox.