In "Fahrenheit 451", how does Beatty attack and argue with Montag? What is Montag's reaction?
Beatty takes a multifaceted approach to arguing with Montag; I would liken him to a father or older brother.
Beatty is usually calm and authoritarian when discussing these subjects with Montag, demonstrated by actions such as smoking, which usually implies that a casual conversation is being held. Beatty also relies on the authority of the government to back him up, such as when he doesn't bother to contradict Montag's idea that firemen once put out fires, instead allowing his subordinates to demonstrate it for him. He alternates this authoritarianism with what seems to be an honest, personal touch, confiding in Montag various secrets such as the fact that he himself has read books as well. Beatty has "been there" and come out the other side with the conclusion that books are dangerous, so what harm could it be for Montag to dip his toe in these waters, as long as someone like Beatty is there to guide him?
Nevertheless Beatty has a constant threatening undertone, and even the most innocuous of his lines tend to have an implied tone of suspicion or the promise of punishment if Montag doesn't behave.
Montag tends to react with restrained curiosity and poorly-veiled rebellion (hence Beatty's suspicions). This culminates in Montag murdering Beatty, and in this scene we can really see how weak Montag is compared to him; Beatty is not only more well-read than Montag, but more in control of both himself and Montag as well. It seems as though Beatty might have been grooming Montag to kill him and escape, considering himself to be too far-gone to be worth saving, or perhaps he simply saw Montag as a "useful idiot" who could pull the trigger and give Beatty the exit he wanted.
Beatty is sneaky about arguing with Montag. He doesn't really argue with him; rather, he tries to play the "I'm just like you...we're chums" approach, but there is an underlying aggression to it. He plays the role of wise informant-"Tell ya what, kid, I'll let you know all about books, see?" However, he laces his "lessons" with warnings. He warns Montag that scratching an itch for a book is okay, as long as he returns it quickly.