Outside Cat to Inside Cat

Is it possible to convert a cat that's used to being outside to an inside cat? I've heard rumours that you can,but I would tend to think once it's had a taste of the outside that it would be difficult if not impossible to make this change.
Reason I bring this up is when we originally fostered this cat from the shelter,it wasn't made clear to us whether the cat had been outside before and he has been seeming really antsy like he wants to go outside. He'll do things like caterwaul alot in the house,sit by the window for awhile, then try to go inside the closets near the window indicating he might think it's a way out. He also tries to come down the stairs to the front door when he hears it.
The reason we don't want him outside is that we live in the city and it's especially dangerous...also the first 'neighborhood' cat my wife liked got ran over here outside.

Its very possible, I've done it myself with a few of mine. Is he neutered? It sounds like he's not if he's caterwaulling. If he is neutered then maybe he just needs some more toys and play time with you. I'm sure others will come along that have more suggestions.

If the cat is neutered, it won't have as much drive to go out and mate. That doesn't mean it won't try at all. How long has the cat been at your house? It takes a few weeks to get completely settled in.

And just because the cat thinks it wants to go outside doesn't mean you should let it. It's very hard to explain to a cat (or a 3-year-old child, for that matter) about wild and mean animals, cruel people, diseases, and cars.

All the shelter said was that any animals surrendered there are neutered so I assume he is,even though he seems to be behaving otherwise...his urine smells strongly,our female cat won't let him near her,and he seems to want to go outside. He doesn't seem interested in toys or humans that much either.
We've only had him for a month or so.

As far as letting him outside I wasn't sure if it's the same as a child,I'd thought it was more instinctual.

My recently aquired stray acted the same way for a few months after she came inside.
Mostly she asks to go out from habit.

Totally doable, she'd rather stay inside now and not have to hunt and compete with cats and coyotes.

Some tips to keep a previously outdoor cat to indoor only.....
Give them physical challenges, like kitty condos, ramps and high access areas
Give them window perches, a window shelf, preferably carpeted that they can perch in and watch outdoor activity.
Make sure they have plenty daily interactive play
keep their litter box clean
Always be alert when exiting and entering the home to avoid escape

We've tried the toys,the grass,and the window but he just doesn't seem content. Maybe he is in heat then b/c right now the only thing he seems interested in are other animals and trying to get to the front door.

You could double check with the shelter to see if he is in fact neutered. Sometimes you may not be able tell by looking.

Two of mine make a mad dash to the door in an attempt to get out. They were orphaned and have never been out. They only understand that if a door is closed, they must see what's on the other side. Could be a bathroom door or the outside door.

How long has he been with you? It will take some time to adjust. If he gets out he may try to "go home" to the last place he lived.

Just watch the doors and spent time with him. It's not safe there (not in my area either) that trumps everything.

Oh yes, absolutely. May take a little longer 'till he/she gets used to the new environment but it is possible.

Ku Ku was a former "Feral Queen", 100% outside cat when I first adapted her, she was allowed(well, I'd rather say the person who brought her in was allowing her to...) to go in/out. Anyways, to make a long story short, after she got into a fight & came home injured, I decided not to let her out or wondering around any longer. I also had her spayed right after that. Ever since, she became 100% indoor cat. She used to sit by windows a lot and reacted to other cats wondering around outside but she rarely does that these days. Lots of toys, catnip, also feliway spray/plug-in helped a lot.

Some of my best cats are ferral rescues. My husband built an outside run accessable thru a cat door. If you have the set up that is the best of both worlds outside yet totally safe. You definitely need to find out if he is neutered. He will come around. Put a bird feeder outside the window he likes best. Be sure the screen is secure and also use claw proof screening. Don't give up. He has a safe environment now. Be extremely careful of the door. They are soooooo fast!!