Remind him how happy his childhood was and try and get him to think of family holidays together or days out when he had a great time. Then get him to think of how much joy he must have brought his parents when he was younger - wouldn't he like to do the same? Get him into the spirit - decorate the nursery, take him shopping to get accessories such as the buggy and wee clothes. Start to talk about baby names. Get him excited about his new son/daughter entering into the world. He will have his "little princess" or else a son he can teach to ride a bike and play football with. Whatever happens - all the best!!
I don't think the subtle route is going to work. This is a child you'll have to support in various ways for the rest of your lives and it's a big deal so it's best just to be out with the concerns. Ask him why he's reluctant. Maybe you can address some of those concerns. He may think he won't be a good dad or that he doesn't know anything about kids or maybe he didn't have such a happy childhood. Books on being a dad may help too--so he can see that men do this every day and since you chose him to have a baby with, he must be perfectly capable and worth it. But, unfortunately, you may have to be honest with yourself that not everyone wants to be a dad so be prepared for it not to go your way when you talk to him.
Tell him how much it means to you, explain to him how long you have wanted it and what it could mean in your relationship with him. If he truly loves you, he will accept how you feel about it. And if you have explained yourself sufficiently, he will maybe even be excited about the child!!
i do agree with Stella, not everyone wants to be a Dad, some people are very happily childless and you won't convince them otherwise. From the way you have phrased the sentence it sounds like the baby is a reality so he can't just dip out of his responsiblities now!!. Hopefully this was a planned pregnancy and not an accident so he doesn't feel that he has been driven into a corner.
I think when he sees the baby he will probably change his mind, but don't go on and on at him, he will only withdraw, slowly slowly catchee monkey as they say.
cheers