BBQ Invitation - how do I only invite a few people from an office where word goes around really fast?

I am trying to organize a Barbecue with some friends for the fourth of July. I would like to invite coworkers from my previous workplace, but not all of the office, since my resources are rather limited (space + financial). However, I am afraid that word will go around really fast (it's a pretty tightely knit work team) and that people will feel offended for not being invited.

What is the best way for me to single out the people I want to invite without making a big deal out of it? I really would like to see them all there, but that's not really an option.

Thanks for your suggestions!

I appreciate the feedback and apologize if I seem a little pretentious, really not intentional :-S

I'm not afraid about them being devastated, I just don't want the office the invitees to randomly throw out "say, are you going to Mel's party?" and getting this awkward silence.

Make an invitation that expresses that you are "planning a small 4th of July party" and include an "RSVP for space and food planning." That should indicate your feelings. The others that are not invited should be mature enough adults to accept that you could not invite a large lot of people.
Hope all goes well.

Trust me it WILL get around and those not invited WILL find out about it.

You could tell the guests to be discreet when you call to invite them.

But, in the end, you may just have to trust the excluded people to be mature enough to know they can't be invited to everything.

The reality is people have gatherings all the time without inviting everyone from their workplace, and especially a former workplace.

I would contact the individuals you want to invite without using a work phone or work email, and explain to them that while it's certainly not a secret, that this is a small gathering and you aren't able to include everyone you'd like to.

The one way you can ensure word will get around and bad feelings will crop up is if you really emphasize that the invitees should keep it secret.

Just invite over the people you'd want only to come. Chances are, others will have made plans for the 4th anyway so maybe only a few of those will even make it to your party.

Don't worry about it. I'm sure they don't invite you to all of their events, either. Who cares? It's just a barbecue. You might be thinking a little too highly of yourself anyway, if you think that this exclusion will devastate them. As others said, they've likely already got plans, anyway.

You don't invite them in the office, certainly.
You send the invitations to your co-workers homes. Perhaps you can add a note to the effect of "Please ask me before inviting anyone else, even co-workers, as we have limited space."
Also, "If you have questions, call me at 555-7777 and not in the office, Thanks!"