The second one is correct. The first is not. Perhaps you meant to say " I am agreeing with you " , but I'm not sure that this is correct either..

Hi, Mona. Only the 2nd one is correct. "To agree with someone", the affirmative form would be:I agree with you, and the negative: I don't agree with you. As for the 1st sentence, "agreement" is a noun, you can use it like this: I am in agreement with you Also: have an agreement/reach or come to an agreement/make an agreement

The first one should be “I'm in agreement with you.“ The other sentence is right, though :)