That's half true... American Liberalism combines an economic approach that accepts taxation, interventionism, and social justice, with classically liberal views on personal liberties. American Conservatism, on the other hand, has a much more free-market and deregulatory approach to economics, and favors maintenance of commonsense moral standards and traditional social constructs. Libertarians, which are the true "liberals" in the international sense, combine Conservative economic views with Liberal social views. The LCS does favor tough taxes, wage and corporate regulations, and so on. So they aren't Libertarians.
The thing is, even though American Liberals are economically more socialist than the Conservatives, they aren't really true socialists in the international sense. They tend to still have both feet entrenched rather firmly in market economics and don't favor government control of important industries, merely government regulations to ensure that private industry serves public interest. America is a very capitalist country, and even our proponents of government intervention are usually just a different stripe of capitalists. Liberals don't have an opportunity to prove this often, because there's rarely an argument they're on the free market side of; anything Liberals want to have deregulated is usually near-unanimously agreed upon, so there's no argument to be had.