My kids are teens now and I cannot encourage you enough to stick with it, while your son is still little, to build good habits early. I know it's hard but it will pay off later.
Also, if your son is telling you "it's too hard" I suggest that you believe him. The reason he can easily get the toys out becauae he is focusing on one item at at time. Even if he dumps all the toys out all at once, he is still going to pick up and focus on one item at a time to play with. But when he has to clean up, he is looking at the entire pile that has to be put away. Even if you say to just put them away, one item at a time, he may still be looking at the whole thing and feeling overwhelmed (like I do, when I have to straighten up my house!)
One thing you can try is to make a pick-up game out of it. This will require you to be around while he is cleaning up, which is not always convenient for a busy mom, but may be worth trying. First, tell him it's a game that will be fun and get him prizes, and will also give him a clean room at the end. Make it sound like it will be fun. Depending on what kind of items need to be put away, ask him to hunt for one catagory of toys. For example, hunt only for books or only for blocks or for small metal cars. If there are a lot of one thing, like legos or blocks, tell you to hunt only for the red ones or only for the square ones. After all those kind are found and put in the toy box, he gets a treat (described below). Then move to the next type of item, like animals, or animals with fur, or plastic animals. If there are a lot of things, but no clear catagories, you can ask him to hunt for a particular color or a size (find everything that can fit in your shoe).
Each time he hunts down and puts away a catagory, he gets a tiny treat from you -- a slice of a fruit he really likes (and don't let him have it during the day, only at clean up time. Avoid candy, if you can), or give him a hug or do a silly dance together with him standing on your feet. Tell him if he hunts down the items super fast, he gets 2 tiny treats when that category is put away. Then move onto the next catagory and reapeat until the room is picked up.
Of course it is far, far easier for you to just pick the stuff up yourself. Don't do it! Make it a very fun game and keep it up daily for at least 3 weeks. (It takes 21 days to form a habit). After that, tell him that big boys get stars on a calendar for doing a good job and give him one each time he cleans up. Tell him that after he gets X number of stars, he can get a bigger treat of some kind (something reasonable, not expensive or unhealthy). It will take a lot of effort on your part, and it will be SO worth it later on.
You can get other ideas from books at the library on changing child behavor. There at lots of technigues out there to choose from. One thing I can tell you beyond a doubt: positive reinforcement works 1000 times better than punishment. (just like with adults!)
Good luck.