In Modern warfare 3, is the Juggernaut in support pointstreak package only for defensive, IE you can't shoot or attack? I got it briefly but that's what it looked like it only was for, but wanted to verify....
No; you can attack, but obviously less effectively than the Assault Juggernaut. The Riot Shield has a melee attack (bashing), and you also get a USP .45 pistol as a secondary weapon.
The shield is mostly useful for defending (say, a control point), but if you get a couple of team mates to follow you, you can also provide an nigh-invincible distraction and cover for an offensive front.
The Support Juggernaut also has it's own portable radar that goes with it wherever it goes. This is something the Assault Juggernaut does not have. The Support variant is aimed at helping the team, hence why it has a riot shield and a portable radar equipped. The pistol isn't as useful but it can get one or two enemies out of the way at a time. If you and a number of your team mates have Assassin Pro equipped, the Support Juggernaut can become a big threat to the enemy team, because even if your team gets EMP'd or a Counter UAV from the enemy team is put up in the air you can still see enemies not using Assassin because you never lose your radar.