Environmentalists may find little common ground with today's Republican Party, but they have no problem with the GOP of yesteryear. In fact, the leaders of influential national environmental groups in a recent poll chose Republican Presidents Theodore Roosevelt and Richard Nixon as the "greenest" presidents ever, followed by Democrat Jimmy Carter. The ranking released yesterday by the Toronto-based Corporate Knights magazine asked the heads of 12 major environmental organizations to nominate up to three past presidents they believe did the most for environmental preservation during their presidencies.