WASHINGTON — The Justice Department is threatening to withhold millions of dollars in federal aid to local police departments unless they adopt policies that require uniformed officers to wear body armor.

The requirement, which takes effect this month as local agencies apply for as much as $37 million in federal aid to purchase a bullet-resistant vest, comes in the wake of a recent surge in fatal shootings of police officers.

Jim Burch, acting director of the department’s Bureau of Justice Assistance, said the new federal policy is in response to the spike in violence — a 44% jump in fatal police shootings over the same time last year — and research showing that 41% of police agencies do not require their officers to wear body armor.

“What struck us is the number of agencies that don’t have a mandatory policy … a potential huge vulnerability,” Burch said. “If we’re investing federal dollars, we should require agencies to have policies.”

Last year, the Justice Department distributed $37 million to reimburse 4,127 agencies large and small, from Anchorage and Boston to Chicago, New Orleans and Los Angeles, for the purchase of 193,259 vests.

Justice officials began contemplating changes to the vest program after a 2009 review by the Police Executive Research Forum, a Washington, D.C.-based law enforcement think tank, found that 41% of departments do not require officers to wear body armor at least some of the time. The federal program would mandate that officers wear the vests while in uniform.

Among the other findings in forum report, which surveyed 782 agencies: fewer than half of the agencies that required armor had written policies addressing the issue. And the overwhelming majority of the agencies — 90% — do not regularly inspect the equipment to ensure that it fits or has been properly maintained.

“There is no good reason I can think of for not requiring it,” said Chuck Wexler, the forum’s executive director. “This is an appropriate role for the federal government.”

The Justice action has prompted a number of police officials to re-evaluate their own policies or risk losing access to federal aid at a time when local government budgets are being slashed and services, including law enforcement, are being dramatically cut back.

Sacramento Police Chief Rick Braziel doesn’t believe the federal government should dictate how local departments operate, including whether individual officers should be required to wear vests.

Under his department’s policy, all officers must have vests. Braziel said he will now require that officers wear vests, if only to ensure that the federal money keeps flowing. Last year, Sacramento received $45,412 for 360 vests.

“Decisions like these are better left to individual departments,” Braziel said. “But right now we’re scraping for every dime we can get. We’ll be making a quick change (in policy).”

Milwaukee Police Chief Ed Flynn said his department is drafting a new policy to meet the new federal requirements.

“It wasn’t about the money,” Flynn said, adding that he was motivated by the Justice action to focus more attention on officer safety. In addition to new vest requirements, Flynn said there are plans to beef up security at police stations.

Seven Milwaukee officers have been wounded in the line of duty in the past two years. All but one was wearing body armor. But Flynn said officers now need to know that armor should be regarded as necessary equipment.

“It’s a second skin,” the chief said. “It’s part of the job. It’s what you do.”

Alarmed by the spike in officer fatalities, U.S. Attorney General Eric Holder last month convened a meeting of law enforcement officials. He said vests purchased through the federal program helped save the lives of six officers so far this year.

“Our law enforcement officers put themselves in harm’s way every day to ensure the safety and security of the American people in cities and communities across the country, and we need to do everything we can to protect them,” Holder said.