I'm pretty sure that Roth planned it to be a failed hit on Pantangelli, one that would then get that boss to turn on Michael and testify against him, figuring (wrongly) that Michael had ordered his (Pantangelli's) murder. Later, back in Nevada when Michael learns that Pantangelli is alive, Tom Hagen tells him, saying something like, "Roth planned this one beautifully."
The cop that interrupted the hit seemed so innocent and nerdy, you'd think he was an honest officer friendly that stumbled onto an ongoing mob hit. The bar owner seemed to think so - or was he also acting to fake Pantangelli? The cop was almost certainly a fake cop, or a real cop who was paid off, and either way with the job of interrupting the hit.
Also regarding the bartender/owner. Did he know a hit was going to occur? Did he know the cop was a plant and just pretended to be nervous to convince Pantantgelli?
Additionally, after the near hit fails (by design), there is a shootout in the street. This was not staged. Was that more of Roth's plan to convince Pantangelli and his bodyguards (one of whom, Cicci, was wounded) that the hit was real?

It's a case of the filmmakers not understanding the plot of the film they are making.

This is all confirmed by the movie script. It seems almost impossible to pull of but Roth did order / give the go-ahead to kill Frankie 5 angels but also sent a cop to come into that bar at the exact time he was about to be murdered. Roth also wanted to ensure that Frankie was shaken up but survived. Roth was goodreal good
He is based off of the real life Meyer lansky who did successfully avoid jail time and an early deathUnlike his associates Luciano buggy Siegel and many more

My take on it was that Roth wanted the Rozatto's to ALMOST kill Frankie and, in the process, give him the impression that Michael gave the order ("Michael Corleone says 'hello'"). The cop was a coincidence. Of course, there is no definitive proof of this, but it's the way I always saw it.
He who conquers himself is mightier than he who conquers a city.

That's what I thought.
The only thing that made me rethink it was, 'Would Roth have the balls to launch a scheme that intentionally involved a shootout with a NYC police officer'.
Everything else seemed ingenious except for that detail.
http://tinyurl.com/9-simple-easy-guacamole-recip

whole thing was staged by Roth. Basically he ordered the Rosatos to kill Frankie BUT he also arranged for a cop to be there to catch it. basically he was playing everyone. When the assassination attempt failed Roth came up with a new plan. He turned Frankie against Michael by making it seem like Mike ordered the rosatos to kill him. This would allow Mike to go to jail when Frankie testified