WASHINGTON – The Pentagon said Monday it will once again begin requiring anthrax vaccinations for troops heading into dangerous regions, reinstating a program that has been challenged repeatedly because of possible health risks.

Dr. William Winkenwerder Jr., assistant secretary of defense for health affairs, said the vaccinations will begin in 30 to 60 days, and will involve troops, civilian Defense Department personnel and contractors who are serving in the Middle East, Central Asia and the Korean Peninsula.

“This is a safe and effective vaccine,” Winkenwerder said in a conference call with reporters. He said the move to reinstate the vaccine does not suggest there is any new or elevated threat, but the possibility of an anthrax attack is “very real and it has not gone away.”

Opponents of the program promised a fresh challenge. Mark Zaid, one of the lawyers who previously sued to stop the mandatory program, said he would file a new lawsuit “as soon as needles start going into arms.” Other groups who have opposed the program also criticized the new requirements.

“This is a vaccine that is unproven, unnecessary and has the potential to jeopardize the health of a service member where little benefit will be derived,” Zaid said. “It’s always been a public relations program and nothing more.”

Winkenwerder said the vaccine has been thoroughly reviewed and deemed safe by the federal Food and Drug Administration and several independent groups.

He said anyone who refused the vaccine would be reminded of its importance and safety. Then, if necessary, the person’s supervisor would get involved and the matter would be resolved “like any other refusal to follow a lawful order.”

He said that while significant numbers of troops refused the vaccine in 1998-99, very few have objected to taking it since then. About 10 people were discharged for refusing the vaccine in 2004, but he said he did not know how many may have refused and gotten other punishments. He was unsure what would happen if a civilian employee or contractor refused the vaccine.