When in danger, all citizens have the right to self-defense, even involving force against an attacker or potential threat. This is covered by recent Supreme Court rulings giving self-defense the status of "Fundamental Right." However, the use of force for police officers when making an arrest is separated from personal self-defense; police are always considered to be acting in defense of others and putting their own safety aside.
The Use of Force Continuum is a general procedure given to law-enforcement as standards of acceptable force. When making an arrest, a police officer is only supposed to use the level of force allowed by the suspect's behavior. For example, if the suspect is drunk and disorderly, no force beyond verbal warnings and handcuffs is allowed. If the suspect pulls a knife, the level escalates, and the officer is allowed to use non-lethal methods to subdue the suspect, including Pepper Spray or a Nightstick.
The difference between protecting self and protecting others is largely semantic. However, for a police officer, any threat to self is always considered a threat to others; if someone attacks the police, they are far more likely to attack others as well. Therefore, under most interpretations of the law, a police officer would be allowed to use the same standards of the Use of Force Continuum in protection of self as he would in defense of innocent civilians.