Atari 2600 or Arcade Game Questions? Help.

[CZAR]

I am tryin to locate this game and I am not sure if it was on the Atari 2600 or just and arcade game. The way I can descride it is: U start in the middle of the game and then u are surrounded by a lot of creature, aliens etc....and u shoot your way out of it. After u complete the stage u basically do it again but it gets harder and then again u appear in the middle and then several other objects appear all around u and u shoot in all directions to eliminate them and create space. Anyone know which game I am referring to? Thanks. Got Em!!