I have the exact same problem with my 18mth old Jack Russell, he can smell a pup from a mile away! He does the same thing your dog does, chasing, growling, general stand over tactics, no biting though. The only thing i can think of that has caused this, is that he was pounced on and hurt by a few over exuberant large pups when he was younger, so now he has the attitude of I'll get you, before you can get me.
There are some pups that completely dont get the hint and think he's playing and turn and chase him, if they do this he will calm down and play with them.
I'm in Australia where we can walk most places off lead, dog parks are for the runners who bolt when off lead, so I've never been to one. I just have to keep an eagle eye out in the distance for any puppies coming our way, which can be hard with large/giant breeds because they look like adults. I bend down next to my dog and start patting the pup, while holding on to my dogs collar so he doesnt launch, all the while trying not to let the pup get all in my dogs face, it's a very difficult process. Talk in a soothing voice, good puppy, good puppy etc etc If my dog behaves, he gets a treat. I've been battling this for a year, and I'm still at a loss on how to fix this..
3 days ago he tried it on with a 5mth old Border collie pup, I did tell the owner that he's no good with puppies, but they let him approach anyway. Well as soon as my dog grumbled, this pup turned around and launched a full on attack on Nugget (my dog), teeth baring and bit him fair on the bum as he was running away! Now this can go 2 ways, he may think twice next time he sees a pup, or it's made him much worse. We havent seen any puppies, so we will see how he goes..
ETA: He's good as gold with adult dogs. The puppy he hated this year, he'll be fine with next year.