In general, yes. But more specifically the ability score you add to your "to hit roll" and damage roll is dependant on the power you use to attack. In 4e an attack is an application of a power. This is a new concept in 4e. Your class grants you various attack powers, but any PC can also use a "melee basic attack" or "ranged basic attack" power. The "ranged basic attack" power can be used by any PC with a longbow (provided they are big enough, have 2 hands etc...)
Ranged Basic Attack
At-Will . Weapon
Standard Action Ranged weapon
Target: One creature
Attack: Dexterity vs. AC
Hit: 1[W] + Dexterity modifier damage.
Where is says , Dexterity vs. AC this means you attack roll is modified by your Dex Ability Score modifier (and compare your result against your opponent's AC). Incidently, if you are proficient in the longbow you also add +2 (the weapon's proficiency bonus) to your attack roll, because this power has the "weapon" keyword. If you hit you deal damage which as noted is modified by your Dexterity modifier.
However, if you are using a class based power things are different. For example if your PC is a ranger you could use the Careful Attack power:
Careful Attack Ranger Attack 1
At-Will . Martial, Weapon
Standard Action Ranged weapon
Requirement: You must be a ranged weapon.
Target: One creature
Attack: Dexterity + 2 vs. AC
(ranged).
Hit: 1[W] damage
(note: I have simplified this the power from as it was written in the PHB, as the power works as both a ranged and melee attack)
With this power your "to hit roll" is again modifed by your Dex mod (with a bonus +2), however you do not add any ability modifer to the damage roll (damage is simply 1[W], which is 1d10).
I can't think of any powers applicable for longbows that use modifiers other than Dex, but there may be some (either now or in the future).
Hope that helps!