Harvey Keitel -- Hey E*Trade, Deal's a Deal ... Gimme My Cash

Harvey Keitel played "The Wolf" for E*Trade -- swooping in to save its ass in a commercial series, only to have the company yank a $1.5 million deal out from under him ... according to his lawsuit.

Keitel says E*Trade came to him in early 2014 ... desperate to land a new spokesman, after Christopher Walken turned them down twice. Negotiations were fast and furious, and they agreed on a 3 commercial deal -- he says the company sent him the contract, and he accepted the terms.

But 2 days later, E*Trade informed Keitel it was "moving in a different direction" with their ads. He says there was no further explanation, but they did offered him $150k ... as a kill fee.