Statistically speaking, it's probably harder. I don't have any hard facts to back it up, but I suspect that there's a trend in America for white people (including women) to seek white partners, and for black people to seek black partners. I mean, the same reasoning would hold for any ethnic group, not just whites and blacks. That said, I really doubt that it's going to be impossible for you to find a (white) woman you like, who likes you back. I have a friend who is a white woman, and she's totally cool with black guys. The only guys I've ever heard her talk about are black guys.

In sum, I'm sure there are lots of white women out there who'd be cool with having a black man as a partner. As a white man myself, I can't say I know what your situation is like, but if you just try to interact naturally with the people around you, how could you fail? It's all you can do, anyway, right? It's not like you're going to come up with some magical plan for landing the woman of your dreams; you just have to interact with people proactively but naturally, and it'll happen somewhere along the way.

G'luck.