I'm not a gun-lover, but I think it is important for officers to carry firearms. They should carry tasers as well. Those can effectively take down an opponent who has a knife, but without the firearm, it would do nothing for gun-toting criminals.
A pistol is not too excessive because they are not automatic weapons, but are effective at handing most situations where an officer's life is at risk. Or what if you had a situation where they had another's life at risk? If they only have a matter of seconds to act, their precious radios wouldn't do much good. A truncheon, or even an air taser would not be very effective at neutralizing the criminal before he kills a hostage or the officer himself.
It's like Rosevelt once said "Speak softly, but carry a big stick." This works well if the intent is to not use the stick/gun, but just carrying them would give more leverage in a situation. They can be dissuasive enough that people would not seek to challenge an officer. Just in case that's not enough, they still can call for backup.
I am not for everyone else carrying weapons, especially assault riffles, but this is too idealistic to ever be a reality. The only way to ensure the law is kept is to give officers all the means to protect both themselves and others. For that, they need both pistols and training in the use of non-lethal weapons.