I've noticed (empirically) that American players tend to be weaker than Israeli players with comparable non-international ratings. Is there a tool for converting one country's Elo rating to that of another? Or of otherwise verifying this claim?
When you say 'comparable non-international ratings' do you mean USCF ratings? Or perhaps Israeli ratings? There is no valid way to compare the ratings of players if they don't use the same rating system. Even if they use the same system things can get odd when groups of players are isolated from one another.
While ELO isn't perfect (what is?), players' ELO ratings can be (and are) compared directly. There is still the 'pool' problem especially at the lower levels but at least the system is the same.
Edit - my answer makes the assumption the entire ratings lists of both countries aren't available. If they are available, a mathematical approximation can be made. It will not be very accurate for the ends of the bell curve. For example, I would not use this to compare the strongest GMs in each country.
50 % answer, 50 % comment on Tony's answer: While it is true that the ratings of different rating systems are not directly comparable, there is always a very high correlation between players' ratings in two systems, and someone with access to the data should be able to get an approximative conversion formula. With hard work, you might be able to google some approximations (I didn't find anything more than forum discussions without any sources). For example, many national chess federations use some chosen formula to convert the Fide ratings of foreign players to initial national ratings.