Washington ? Middle-aged Americans probably remember it as little more than a ho-hum trip to the family doctor, but the resumption of large-scale smallpox vaccinations after a 30-year hiatus promises to be anything but simple.

The Bush administration is expected today to set in motion plans to inoculate 500,000 military personnel and up to 500,000 health care workers nationwide — the front-line defenders in any biological warfare attack against the United States.

As more vaccine becomes available, federal health officials say the initial program will soon expand into a second phase to include 10 million to 12 million additional Americans — virtually the nation’s entire contingent of police, firefighters and other first responders. Vaccine would probably be offered to the general population by 2004.

States, cities and territories have been getting ready for the first phase of the program for months, calling for volunteers, educating them on the vaccine’s dangers and preparing to monitor its effects. Wyoming conducted drills to determine how long it took to vaccinate 100 people.

“We are extremely pleased and quite impressed with the plans that have been submitted so far,” Health and Human Services Secretary Tommy Thompson said Thursday. “It is obvious the state and local health departments and hospitals have stepped up to the plate under an extremely tight timetable.”

The military plan, unlike the civilian version, is mandatory, according to a key congressman, but in other respects will largely mimic civilian procedures ” vaccinating first-line medical personnel before immunizing soldiers in high-risk areas like Iraq and the Middle East.

The smallpox vaccine, used routinely throughout the United States until 1972 and in the U.S. armed forces until the 1980s, can have extreme side effects. For every million people vaccinated, up to 52 will suffer serious illness, and one or two will die.