2 black labs 3-1/2 behavior

Question
Have had these 2 brothers since pups - good dogs - won't bite, won't attack, very friendly - except when I have them in the car and they see another dog walk by they bark, growl terribly like they would eat them up - out of control - if I open the door they immediately change behavior to total "friendly" in the car people are scared to death of them.  If you walk up to the car, they wag tails and they are very friendly dogs.  How to STOP this behavior if a dog walks by the car.

Answer
Unfortunately, if you want to stop this behavior, you will need to see a trainer that will work with you one on one WITH the dogs.  This is not really best addressed through a web based advice board.  

Dogs get territorial when they are secured (leash aggression, fence aggression) and this can translate to the car as well.  You can try to google training tips on aggression.

This link takes you to a similar question/answer:  http://en.allexperts.com/q/Canine-Behavior-3553/2009/3/aggressive-car.htm