WASHINGTON (Reuters) - Up to 450,000 doctors, nurses and other health care workers are ready to be vaccinated against smallpox when President Bush gives the go-ahead, the U.S. Centers for Disease Control and Prevention said on Thursday.

Bush was expected to give details of the plan on Friday. He is expected to say 500,000 troops and nearly as many health care workers will be the first to get the vaccines.

Under plans submitted to the Health and Human Services Department by other experts, another 8 million or so health care workers could be vaccinated later, with the vaccine eventually being offered freely to the public as it becomes available and licensed.

The CDC asked states to submit detailed plans on who would be vaccinated in the first stages of the plan and how.

"So far, 49 states and four cities have submitted plans," the CDC said in a statement.

"These plans contain information on the number of people comprising each public health smallpox and health care smallpox response team, information on where vaccines would be administered, the number of health care facilities identified to participate, and the number of clinics needed to support this effort."

It adds up to 450,000 people who are ready to be immunized, the CDC said. These would all be volunteers and carefully screened in an effort to minimize the side effects from the vaccine, which is considered crude and dangerous.

Based on the earliest known vaccine technology, the vaccine kills an estimated one or two in every million people who get it and sends at least a dozen more to the hospital with serious illnesses such as encephalitis.

Today's population may be even more vulnerable to such side-effects, the CDC says, so the agency is urging careful choices about who gets the vaccine.

Recent polls, including one published by the non-profit Robert Wood Johnson Foundation on Wednesday, suggest more than half the adult population would like to get the vaccine.

Smallpox was eradicated in 1978 but the government says there is a risk it will be used in a biological attack by terrorist groups or perhaps Iraq.

"The plan is voluntary and eligible individuals will make their own decision on whether or not to receive the vaccine," the CDC said.

"Hundreds of clinics around the nation would be set up to deliver the vaccine to those who choose to receive it. In addition, state health officials have identified over 3,300 health care facilities that would participate in the program."

Those to be vaccinated first would then be protected and able to vaccinate wider numbers in case of an attack.

"The development of these plans is fundamental as we prepare the public health system to respond to an intentional release of smallpox," CDC director Dr. Julie Gerberding said in a statement.

"By protecting individuals who would initially be called upon to respond we increase the capacity of the public health system and the nation's hospitals to control and contain a smallpox outbreak."