SPRINGFIELD - Springfield police officer Kevin Fitzgerald was not wearing a protective vest when he was stabbed in the chest today, but police officials said a bullet-proof vest may not have made much of a difference against a knife.

The vests are designed to absorb the energy of a speeding bullet, but in some instances, vests have been found inadequate to stop sharp, pointed blades, officials said.

Fitzgerald was stabbed this morning at 47 Knollwood St. as he and another officer responded to an ambulance call for a 14-year-old boy who refused to get out of bed.

The boy lunged at Fitzgerald with a 4-inch kitchen paring knife, striking him in the chest. The knife went in up to the handle, police said.

Fitzgerald was in fair condition last night at Baystate Medical Center.

Springfield police said Fitzgerald, a 20-year-veteran assigned to the uniformed division, was not wearing a bullet-proof vest.

Sgt. John M. Delaney, executive aide to interim Commissioner William J. Fitchet, said the department issues protective vests to officers, but officers have the option to wear them or not.

Delaney said, the majority of officers, he estimated 95 percent, regularly wear vests while on the street.

He estimated most uniformed officers wear them regularly, while officers in the plain clothes bureaus wear them only when on specific details, such as serving a warrant or executing a narcotics raid, he said.

Delaney, who had led the department's Safeguard Unit, said he always encouraged officers under his command to wear their vests.

But, he added, "I can't fault Fitz for not having it on. He chose not to."

Other area law enforcement agencies also do not require vests be worn.

Trooper Thomas Murphy of the Massachusetts State Police public affairs bureau said across the state, troopers have the option.

"We are encouraged to wear them year round and as often as possible," he said.

West Springfield Police Chief Thomas E. Burke said yesterday that the department provides vests to all of its officers in the department, including himself.

Officers are encouraged to wear them for all calls, but it is not mandatory, Burke said.

"It's a personal decision," he said.

Burke, Delaney and Murphy each questioned whether a vest would have even made a difference.

When a bullet strikes a vest, the slug flattens out like a mushroom as the fibers in the vest absorb the bullet's energy. Depending on the knife blade, the point will simply pass though the fibers in the vest, Delaney said.

As Burke said, "The blades can be pretty thin."

The Department of Justice's "Selection and Application Guide to Protective Body Armor," carries the same warning.

"Concealable body armor is potentially vulnerable to knife attack; hence, all officers should exercise caution when confronted in these situations," the guide notes.

Springfield's policy is not unheard of in law enforcement.

According to Department of Justice statistics for 2006, body armor while on duty is mandatory for about 60 percent of departments nationwide. In 1990, it was around 30 percent.

Eighty-three percent of all departments provide protective vests to officers, and another 5 percent provide officers cash allowances to purchase their own, according to the report.