Why did Roth try to have Pentangeli kileld right away? Is it becuase if he was kept alive any longer, Roth would assume that Michael would figure out it wasn't Pentangeli that ordered the "hit" on Michael? or is it becuase they just simply had beef with eachother?

Also killing Pentangeli(a high ranking member in the Corleone family); wouln't that signal a war immediately? Like roth must know if he tried to take Pentangeli out, Michael would come after him right away (which he did) but Roth didnt know that.

Probably because it was so hard to get to Frankie and the meeting was the perfect opportunity. Also, there were any number of variables that could have intervened.

Roth set up the Tahoe massacre so that Michael (or his survivors) would think Pentangeli was behind it. When Michael visited Roth in Florida, he led him to believe that: "Frank Pentangeli is a dead man--you don't object?" But when, instead of killing Frankie, Michael dispatched him to settle his problems with the Rosatos, Roth knew Michael didn't blame Frankie for Tahoe--meaning that he might blame Roth.

So Roth went to Plan B: Lure Michael to Havana, get the $2 million from him and have Michael killed. Just before that, he had the Rosatos attempt to kill Frankie. He did it because he would eliminate Michael's strongest ally and subordinate in NYC--his muscle. He wasn't too worried about the fallout from Frankie's murder because he assumed that Michael would be killed in Havana, and the Rosatos would have to deal with whatever fallout fell on them in NYC.

This raises a point which has always been a niggle at the back of my mind. If the Rosatos' failed attempt on Pentangeli's life was genuine, why would they even bother to give him the impression that Michael had ordered his death? Surely they could not themselves have been under any such illusion?

Granted, the cop walking in at the wrong time seemed genuine enough, but the rest of it seemed like a setup to sow discord among the Corleone ranks in NYC. Perhaps Pentangeli was supposed to survive the attempt on his life, one way or another, for this very purpose?

Hi! This has been discussed a lot. As you likely already know supposedly that was an ad lib that the actor put in which FFC liked and kept.

As to why it made sense within the storyline there are two ways it worked.
1) The Rosato Brothers were mocking Frank at his last moments. It's like telling a devout Christian who is being fed to the lions "Where is your God now?" or telling someone "When you get to hell, tell them I sent you there."

2) It's doubtful that Roth tells the truth to anyone. He may well have told the Rosatos that Michael had given them the ok. I don't think Pentangeli was meant to survive.

Heh, I doubt there's much that hasn't yet been dissected and analyzed here (and probably repeatedly so over the years!)but it's good to see some other takes on this particular topic as it has always stuck in my mind. Thanks for that.

All considered, I think 2) is the most plausible explanation after-the-fact (ad lib aside!). Roth was certainly a great schemer and could probably quite easily convince the Rosatos that the hit had Michael's approval. And, since Michael was also supposed to die, who would be left to say that was not actually the case? Yep, that would have worked quite beautifully . . . had it actually panned out as expected.

I believe Turnbull said it best when he pointed out that likely the line "Michael Corleone says hello" wasn't meant for Pentangeli but meant for the barkeep (Richie? I forget his name). That way later when questioned by the cops, he could say that the killer said "Michael Corleone says hello", and boom Michael now has all sorts of legal trouble.

Thanks, Wayne.
Richie obviously was a civilian, and he was scared of what was happening ("Carmine--NOOOOO!"). The Rosatos knew Richie would be questioned by the cops. He'd be terrified to rat out the Rosatos, so they gave him something to feed to the cops: "I didn't know the guys who did it, but one of them said, 'Michael Corleone says hello.'" That'd set the cops after Michael; and even though he had an alibi, the investigation and possible publicity would be another crack in his "legitimate" facade.