A long-discussed bike-share program in Portland took another incremental step forward on Thursday when city officials asked vendors to help explore options and potential costs of launching a citywide system. Bike-share programs offer communal bicycles that are available to the public or to program members for short-term use. In most major programs, users pick up and drop off the bicycles at specific “bike stations” for a fee. The programs have surged in popularity in many large cities such as Washington, DC, and Boston and are hailed as a way to reduce vehicle congestion and related pollution while encouraging healthy lifestyles.