(01-16) 23:44 PST WASHINGTON (AP) --

The Bush administration says smallpox vaccinations of thousands of health care workers will begin next week as planned, despite protests from two large unions that argue a delay is needed to address safety concerns.

The smallpox vaccination program, announced last month, has come under scrutiny from workers, hospitals and some state health officials, who worry they won't have time or money to do it right.

On Friday, the Institute of Medicine planned to release a report advising the administration on implementation of its plan. When they met last month, several members of that panel, mostly academics from schools of medicine and public health, were also critical of the Bush plan, fearing it was being put in place too quickly.

On Thursday, two large unions argued that there are not enough safeguards in place to make sure people at higher risk of injury are not vaccinated. And they complained there is nothing in place to adequately compensate people who are hurt by the vaccine.

"Health care workers across the country want to be prepared if a smallpox outbreak occurs," Andrew L. Stern, president of the Service Employees International Union, which represents 750,000 health care workers, wrote President Bush on Thursday. "But it is wrong to ask them, their patients and their families to put their health at risk while you have been unwilling to make the plan as safe as possible."

Similar concerns were registered by the American Federation of State, County and Municipal Employees, which represents 350,000 health care workers.

Despite the critiques, the administration is ready to move ahead, said Jerry Hauer, assistant secretary for public health preparedness at the Department of Health and Human Services. The plan calls for vaccinating 500,000 health care workers in the program's first phase.

Hauer said the administration was working to address the unions' concerns, and he said he has full confidence that states will carefully screen and educate patients.

Vaccinations are set to begin in at least some states on Jan. 24, when a law protecting people administering the shots from lawsuits takes effect. Mandatory vaccinations for U.S. military personnel, expected to total about half a million, began last month.

The IOM report was commissioned by the federal Centers for Disease Control and Prevention, which said it needed advice in implementing the vaccination plan.

When he announced the vaccination program, Bush said it was needed to steel the nation against a bioterror attack, even though he said there is no imminent threat that smallpox, last seen in 1977, will return.

The first wave of vaccinations are recommended, though not required, for health care workers and people on special smallpox response teams -- those most likely to encounter a contagious patient.

Because it is so risky, the vaccine is not recommended for the general public.

Experts estimate that between 15 and 43 out of every million people being vaccinated for the first time will face serious complications, and one or two will die. The vaccine is particularly risky for pregnant women and those with a history of skin problems or compromised immune systems, including people with HIV, cancer and organ transplant recipients.

The government plans to carefully screen people so no one in these groups is vaccinated. But the unions fear the screenings will not be adequate, particularly given that most states are in financial crises and there is no federal money designated to run the smallpox programs.

"We just want to be sure workers don't come up on the short end of the stick," said Barbara Coufal of AFSCME.

She said one of the union's largest locals, in Philadelphia, voted not to participate in the program until issues of screening and compensation for people who are injured are worked out.

As it now stands, people who are injured may not be fully compensated for time lost from work or medical injuries. Some will have access to state workers' compensation programs, but those programs may not cover all expenses.