Liverpool fell behind after just four minutes as goalkeeper Alisson diverted a Pablo Fornals corner into his own net under pressure from Hammers defender Angelo Ogbonna, a challenge which survived a lengthy VAR check after Pawson initially allowed the goal to stand.
Fornals and Kurt Zouma both scored within eight second-half minutes before substitute Divock Origi struck late on as the Hammers held on to a victory which takes them above Liverpool into third place in the Premier League table.
Liverpool surrendered a 25-match unbeaten streak in all competitions and Klopp focused his anger on Pawson after the match.
"It is a clear foul on Alisson. How can it not be? The arm from Ogbonna is there. You always have to say the ref maybe in the game can see it but when you see the dynamic of the whole situation, when they all go down, how close they are," he said.
"They are in each other, how can that not be a foul already without pushing the arm of Alisson?
"But the ref made it easy for himself and thought: 'Come on, let's see what the VAR is saying.' VAR had a look and said: 'Not clear and obvious.' I don't know why, and gives the goal which is really strange.
"Then I saw the situation with Hendo [Jordan Henderson] and Aaron [Cresswell] and the way I saw it, it is a clear red card. There is actually no discussion possible and again, I don't know, they will probably say because he touched the ball before.
"But a reckless challenge, you can touch whatever you want before, if you cannot control your leg that much and you hit your opponent high up the leg, you cannot go like this in a challenge. But we cannot make these decisions obviously and the ref, I don't know what he would say about that now but in the game, he looked quite confident his decisions were right."
Infuriated further by another incident in which Said Benrahma appeared to catch Alexander-Arnold after he released a shot, Klopp suggested Pawson had changed his refereeing style to adopt a more safety-first approach.
Asked if referees were relying on VAR as a back-up plan, Klopp replied: "Not all refs. But he does. Not all refs, it is just the situation. He thinks: 'OK, let's see what he says so I don't miss it.' He did that today, definitely.
"There was another situation with Trent Alexander-Arnold after a set-piece, the second ball he takes the ball on the volley, goes down, it is not a foul but he has a proper bruise under his foot. So where is that coming from?
"So it is just, 'don't do anything, let's see what VAR is saying' and then we have a problem with clear and obvious mistake because whoever is then there, hides behind that phrase and then we have two people hiding and in the end we have the wrong decision."
Klopp also hit out at West Ham's approach, adding: "Obviously West Ham plays really good stuff this year, this season but today it was a bit more like the old West Ham -- sitting deep, going for set-pieces and counterattacks."