when you 1st start the game just about any drop higehr than you could jump would kill you but later on drops 5x the hight of what your character can jump wouldnt even give any damadge

so what stat / perk effects this ???

Well, unlike some other games, health damage from falls in Fallout 3 is not a percentage of your health; so having more health helps there. Not sure what else helps.

Your health and DR. Using Med-X before jumping off a bridge will greatly increase your chance of survival.

So if I want to jump off a high cliff and survive all I need is to inject myself with some morphine?

i never use med x unless im up against 3 supermutants with tribeams (broken steel dlc)

+ i dont level up health untill i get teh perk that makes everything 9 .... so why is my level 9 character surviving falls my level 1 characters cant ???

You gain health every level plus you could have increased your character's DR through quests such as by gaining the Barkskin perk or by picking Toughness at level up. The DR from your armor counts too.

Edit: @Sesame- Try some Ultrajet too for extra fun

And Agility.

if jumping from really high (and i mean REALLY high) cliffs is your thing, try jumping, pausing when you think you're a safe distance from the ground, saving the game (always use a new save, just in case), dying, then loading the game and voila! you survived the fall. =)