My 78 has a similar situation with the drivers door. The smog checker guy couldn't get the drivers door open this smog check or during the check two years ago. It did happen to me when I first got the car. You pull the handle and the door is still latched. I found that I wasn't pulling the interior handle far enough out (although it seemed it should have been far enough). I don't have the problem with the outside handle as you do though.
Once you get the door open, check the striker bolt for signs of the latch scraping on it. If it has those signs, your door is not aligned properly. When you close the door does is close smoothly or does it have to be slammed shut? It could be, but hopefully not, your door hinges.
First try lubricating the area. But from what you described, the latch isn't releasing from the stricker bolt. Either bad lubrication, handle not pulling the latch open enough or door alignment. That's the order I'd check.