You can ask for identification and any officer pulling over a car should be in uniform or have some sort of department issued ID with them.
A couple things, some people on here are giving very bad advice.
1. When you see a police car behind you with lights on, you pull over as soon as it is safe to do so. An officer might give you some leeway in driving a few hundred yards to a parking lot or off ramp. But he is not going to tolerate you driving several miles while you attempt to confirm their identity over the phone. Not pulling over is a crime and will result in a $200 ticket from me or possibly being arrested.
2. 911 is for emergencies only. All police departments have non emergency numbers that can be obtained from 411.
3. Locking your door and only cracking the window is fine. But keep in mind that officers have the authority to order you out of the police car during traffic stops (some officers routinely do all the business with you outside of the car or even in their car). Refusing to exit the car when ordered can get you arrested.
4. Asking for a marked patrol is alright. But I wouldn't except to get one, since in the state of Missouri there is no legal requirement for you to have one. An officer can request one, but if all district cars are busy, he's not going to sit around waiting for one to be freed up. Again, delaying/refusing to cooperate can result in you be arrested.
I understand the fear of police impersonators. But keep in mind that out of the thousands of car stops done every day, only an extremely tiny percentage are police impersonators and while the officer and courts might give you a little leeway in driving a bit longer, calling to confirm and all that stuff; I would not expect the officer to have infinite patience with you and if you screw around too much, you can be arrested and have your car towed.
Some tips to help you:
Be educated about law enforcement in your area. Attend a civilian police academy, do a couple ride alongs. That will greatly help you understand how things are done and why. It will also you see how things are done. That may help you identify a police impersonator on your own.
Have local police and highway patrol programmed into your phone. So if you do have to make a call, you are not tying up the emergency line.
Explain to the officer clearly that you want to cooperate, but you have to check things out first. If you are polite to the officer, he is going to give you more leeway. Merely refusing to roll down the window or telling the officer to wait while you are making are a call are very bad ways to start off an encounter.
If you absolutely have to drive ahead to a better lit/ more populated area before pulling over. Give the officer a thumbs up out the window, flip on your hazards, something to signal to him that you acknowledge that you are being stopped and want to cooperate.
You wouldn't believe the amount of people we deal with that think they are in their own little world and the police are supposed to work around that. That simply is not the case.