Despite growing unease among health care workers, and a new report counseling caution, the Bush administration plans to ship its first batches of smallpox vaccine to states on Tuesday, launching a program to immunize local "first response" teams against a bioterrorist attack.

"We need to do what we need to do, which is to get this show on the road," said Dr. Julie Gerberding, director of federal Centers for Disease Control and Prevention, in a telephone press briefing with reporters.

Both homeland security and national defense concerns dictate that the voluntary vaccination program proceed quickly, she said.

"We are in fact living in a dangerous world, where a smallpox attack is possible," said Gerberding, whose agency is overseeing the program.

Initial shipments of vaccine to 11 states that have requested the first doses are likely to begin Tuesday, Gerberding said, although she refused to identify which ones -- saying it was up to individual states to disclose such information. California is not one of them, according to California Department of Health Services spokesman Ken August.

Concerns about the safety of the vaccine -- which has not been widely used in three decades and can cause life-threatening complications -- have led some hospitals to opt out of or minimize their participation in the first phase of the program. The "first response" phase goal is to vaccinate 500,000 medical volunteers, who would be the first to encounter patients infected in a smallpox attack.

Their job would be to isolate and treat those patients, and carry out a mass vaccination program of the surrounding population.

In San Francisco, public health officials have opted for minimal participation, seeking to vaccinate 20 to 40 public health workers who would serve "to vaccinate the vaccinators" should a rapid scale-up be necessary, said Dr. Susan Fernyak, director of communicable disease prevention at the city Department of Public Health.

Had the city followed guidelines adopted by a CDC advisory committee, vaccinations would be sought for up to 225 health care workers at San Francisco General Hospital during the preliminary round.

Lorraine Thiebaud, vice president of Local 790 of the Service Employees International Union, which represents nurses at the city's public hospital, said attitudes among the staff there are firming against the vaccinations. "We're probably less willing to go ahead and do this," she said.

Aside from safety concerns, employees sense the decision to vaccinate is not driven by medical concerns. "This is purely a political thing, tied to the war (against Iraq)," she said.

A sampling of hospitals in neighboring counties found more acceptance of the vaccination program.

While Gerberding stressed the urgency of implementing the Bush administration's plan, on Thursday the SEIU and the American Federation of State, County and Municipal Employees called for a delay in the program -- until details over safety, and compensation for lost wages and injury to volunteers, are settled.

On Friday, the prestigious Institute of Medicine weighed in, issuing a report that -- while avoiding direct criticism of the Bush program -- found numerous problems with it.

"Given this profile of high vaccination risk and possibly very low to zero benefit, the administration's policy to offer vaccination to public health, medical and emergency workers must be implemented in a most prudent and cautious manner," the report said.

The Institute of Medicine convened a committee to examine the program at the request of the CDC, and presented its report as a letter to Gerberding. In pressing its argument to "proceed cautiously," the panel said that the smallpox vaccine "may be the least safe vaccine ever used on a wide scale," and raised concerns that volunteers might not be compensated for the consequences of adverse reactions.

But in her comments to reporters, Gerberding said, "We are not going to delay this program because of concerns about compensation."

Gerberding said that the initial volunteers would be workers, and that various state workers' compensation programs would address the needs of anyone injured.

But in a later telephone interview, SEIU President Andy Stern responded angrily. "It's just outrageous," he said. "Pharmaceutical companies are immunized against the risk, and hospitals are relieved of any responsibility. The best thing an injured worker gets is a get-well card."

Meanwhile, public and private hospitals in the Bay Area are debating just how much to participate in the initial phase of the program.

San Mateo County hospitals are preparing to inoculate as many as 2,000 health workers, said Dr. Scott Morrow, the county's health officer.

Stanford Medical Center, in neighboring Santa Clara County, also plans to participate and has submitted the names of its volunteers to the county health department, said Stanford hospital spokeswoman Susan Ipaktchian.

In the East Bay, Alta Bates Summit Medical Center is working with the health departments of Berkeley and Alameda County to prepare vaccinating workers.