While tolls, bonding and the budget have dominated this legislative session, a battle has been quietly brewing over the creation of a state-administered health insurance public option for small businesses. That fight is about to burst into the open as the session heads into its final weeks. It pits GOP lawmakers and some of the state’s most powerful lobbies—big insurers based in and around Hartford and the Connecticut Business and Industry Association (CBIA)—against state Comptroller Kevin Lembo, Democrats who control the General Assembly, and patient advocates. Backers say their legislation would provide small businesses with a desperately needed alternative to increasingly unaffordable commercial plans, while injecting greater competition to force down prices. Opponents counter that a public option would harm the state’s insurance industry, potentially leading to job losses.