New tax breaks are available to anyone who wants to help the environment by purchasing fuel-efficient hybrid vehicles. But if owners of small businesses really want to save money, they can get even bigger federal tax breaks by buying the largest gas-guzzling SUVs. The disparity is drawing criticism from environmentalists and the Republican chairman of the Senate's tax-writing committee, who is working on a change. Dealers and owners who have benefited from the SUV tax incentive say it helps spur a key part of the economy — auto-making — and allows small business owners to purchase vehicles that improve their bottom line.