Standard US doctorine is to use at least one unit-size up from what the enemy has.
If the enemy has a fireteam, you attack with a squad.
If the enemy has a squad, you attack with a platoon.
If the enemy has a platoon, you attack with a company.
If the enemy has a company, you attack with a batallion.
And so on.
In case you don't know how many men are in a fireteam/squad/platoon/etc, here is a very easy way to figure it out: Each unit type is made from 3 smaller unit types. Actually that isn't exactly true, but it is close enough. So a squad is made of 3 fireteams, a platoon is made of 3 squads, etc.
So if you always attack with the next unit size up from the enemy, that means
you will attack with at least 3x as many men as the enemy has. In your case, that means about 90 NATO troops (about 7 squads), with a few tanks supporting them. That's roughly a company of men, attacking a platoon of enemies.
Remember; not all those men are going to be running at the town at once. Some are going to be providing rear security to counter possible enemy reinforcements (maybe 2 squads), and some are going to be positioned to cut off any enemies that may retreat (maybe a squad broken into teams to cover each escape route; including some snipers).
I would suggest that if the player is in charge of the operation, you give him radio options to call for some of the guys providing rear security to come and help attack the town. However you also should have some enemies try to reinforce the town from outside, so if you call some of those guys in, the remaining guys on rear security might not be able to fight back those reinforcements. Same idea with the guys watching for retreating enemies; if they get called in to help attack, enemies might escape the city, resulting in a failed objective, or maybe those enemies regroup and counter-attack the city.
Another thing to keep in mind is that the US almost always has either
artillery and/or
airsupport. Since they are attacking a city, there should be civillians around that you don't want to kill (definately should be included), and you don't want to destroy their city even if they aren't around. So artillery would likely be out of the question, but there would certainly be air support to take out those tanks.
I'm sure you're thinking "damn, that would make it way too easy"; and that is the idea. We want to lose as few men as possible, so of course we are going to send in an overwhelming force. Just look at the casulty rates during all the recent US confilcts; we kill hundreds of the enemy in one battle, and they kill maybe a dozen of us.
Obviously, if in your mission, the US forces are having a tough fight, then there wouldn't be so many troops to spare, and you could lower the amount of NATO men accordingly. However, what I would suggest you do instead of that, is simply make the defending troops fight more effectively. Check out my "simple cover" script in the pending section of the ed depot, and use that, for starters. DON'T just make a bunch of enemies walk around the town on waypoints. They are defending this town, which should give them an advantage. Walking around between buildings
isn't an advantage. Using well placed defensive cover
is an advantage. It also makes for a more interesting mission.
Check out the simple cover script here:
http://www.ofpec.com/editors/resource_view.php?id=639