Federal health officials have directed the states and the District to speed up plans to offer smallpox vaccinations to 500,000 hospital workers nationwide, urging that the task be completed within 30 days of an announcement that could come as soon as next week.

The timetable, delivered Friday by the U.S. Centers for Disease Control and Prevention, has stirred public health and logistics concerns among state health officials. Most planned to immunize hospital workers in phases over a 60-day period to better track potentially severe side effects.

The advisory, made without explanation, is not linked to an increased threat of a smallpox release, CDC spokesman Curtis Allen said yesterday.

The directive underscores the urgency of a massive public health campaign to vaccinate potentially millions of U.S. residents that top administration aides expect President Bush to order shortly. The voluntary program is expected to start with health workers who would bear the brunt of a smallpox outbreak and would need to be protected in order to treat victims and prevent the health care system from collapsing. Military officials also expect a decision on a plan to inoculate 500,000 U.S. troops.

The civilian program poses complexities unseen by U.S. health workers since routine smallpox vaccinations were discontinued in 1972. The vaccine will require detailed education, screening, tracking and follow-up of a critical segment of health workers, potentially at a time of year when hospital workloads surge and staffing falls because of the holidays, officials said.

"We are struggling with how to logistically phase that in and do it within the 30 days the new guidance provides. It is going to be difficult," said Donald E. Williamson, Alabama's state health officer and the chairman of a vaccination task force.

The CDC's Allen said the change was made "for planning guidance. The ultimate time frame will depend on the announcement we're expecting from the White House." Allen said he did not know why the time frame changed, but called 30 days "a prudent amount of time."

The District, Maryland and Virginia have drafted plans to offer the vaccine, respectively, to as many as 5,000, 8,000 and 12,765 public health workers and private physicians, nurses, epidemiologists and support staff.

In the District, health officials plan to create as many as three, 24-person public health teams that will offer the vaccine to hundreds of workers at 11 hospitals.

Maryland plans to offer the vaccine to groups of 100 employees at 52 acute-care hospitals across the state, Secretary of Health and Mental Hygiene Georges C. Benjamin said.

The state also will organize about 80 six-person public health teams -- one for each hospital and for 24 counties.

Virginia will mobilize about 200 public health workers in 35 districts and offer vaccinations to groups of 45 employees at 90 hospitals, said Jim Farrell, immunization division director for the state Health Department.

Smallpox vaccinations are complicated because of a small risk of severe side effects that appear within three weeks and because the inoculation site can be contagious. Many states planned to vaccinate 20 percent to 30 percent of hospital workers at a time to give clinicians more experience with side effects. States also sought time to train and vaccinate the vaccinators.

"We need the ability to learn about the reactions in a controlled way with a smaller group initially. The phased groups would help us from a public health point of view," said Michael Richardson, director of the D.C. Health Department.

Nationwide, the CDC has set a Dec. 9 deadline for states to turn in plans for carrying out a voluntary smallpox vaccination program that would begin with 500,000 frontline health care workers, expand to 10 million emergency responders and extend to the rest of the population as early as 2004. States have until Monday to outline more generally how to vaccinate their populations within 10 days of an actual outbreak.

The vaccine is estimated to be lethal to one in every 1 million recipients and to require long-term care in one in every 1,000. Smallpox kills about one in three people exposed.

The vaccine's side effects, such as swollen, red arms, will also be unfamiliar to most practitioners, even if the reactions are relatively benign. A slower phase-in would give physicians more experience and reduce unnecessary referrals to specialists. "We're just not used to seeing people have these kinds of reactions," Benjamin said.

The change comes as health officers in the Washington area and across the country prepare to execute an immunization program that dwarfs their response to such recent crises as anthrax, the West Nile virus or the pfiesteria piscicida bacteria.

Vaccination teams must be staffed to screen patients, inject the vaccine, instruct patients on treating the vaccination site, enter data and provide security.

To vaccinate all 5.3 million Virginia adults within 10 days, the state estimates it would need 24,000 workers and volunteers on two shifts at 106 sites, such as high school, university and government buildings.

Maryland estimates it would need 100 to 1,000 workers at more than 30 vaccination sites for 3.9 million adults, and the District has identified 20 vaccination sites for 457,000 adults.

The District's health department is training 200 vaccinators, has enlisted 600 doctors to help and is working with the Red Cross to find more volunteers.

A North Carolina nurse prepares a smallpox vaccination during a training session. Federal health officials asked states to hasten immunization plans.