The FBI also publishes the number of officers killed due to accidents (i.e., no malicious intent). In 2008, only 68 law enforcement officers were killed in accidents while performing their duties in the entire country. The majority of those officers (39/68) were killed as a result of automobile accidents.
Depending on what types of law enforcement officers are included (corrections? sheriffs? BART cops? city? fed?), there are between 430,000 and 800,000 law enforcement officers in the United States [I know I should have a citation for this, but I can't find a reliable source, so I included a range of numbers based on the various stats I viewed]. [Update on 7/20/12: see HERE: "Approximately 800,000 law enforcement officers currently serve across the country."]
109 fatalities (41 + 68) out of 800,000 means police officers have less than a 0.014% chance of dying on the job each year. Of course, this percentage does not include the number of times an officer is assaulted by a perp or random stranger. Even so, law enforcement families should sleep soundly--a 0.014% chance of dying while working means officers have safer jobs than most people commonly think. Of course, that doesn't mean the job isn't tough. Being a street cop is a stressful job, and I wish we'd lower public employees' long-term benefits so we could put the money towards hiring more officers and reducing the number of continuous hours that individual officers spend on duty.
This is no idle debate--the more people who (incorrectly) think officers' jobs are overly dangerous, the more likely the public will allow officers to use excessive force against citizens. Also, if officers overestimate the actual danger they are in, they will use less patient methods of interacting with citizens. That impatience may make you the next Phuong Ho (an unarmed SJSU student who was beaten by police officers because of their failure to properly assess the actual level of the threat against them while Mr. Ho attempted to look for his glasses).
If, however, the public understands that officers have a tough job because they work excessive hours and suffer from sleep deprivation, then we can fix the problem by hiring more police officers, reducing hours spent on patrol, etc.--steps that will increase an officer's chances of accurately assessing the true level of a threat before resorting to force. But without understanding the actual problems of the job, we will focus on the wrong item--danger--which will increase friction between the public and the police as police continue to use impatient, violent methods of subduing/controlling citizens.
Advancing the truth--that police jobs are tough, but safer than people commonly believe--will mean better safety for all citizens, and better mental health for all police officers. Also, the more people who understand that it is rare for an officer to be killed on the job due to their excellent training, the more qualified applicants we will receive. Speaking the truth about officer safety is a fight worth having, even if it's a controversial one.