BOSTON — At a ceremony this week at the Boston General Mail facility, the Postal Service launched the first conversion of a mail-delivery van into a hybrid-electric vehicle. “As an agency that delivers mail to 145 million businesses and households six days a week, drives approximately 1.1 billion miles a year, and consumes more than 125 million gallons of motor fuel annually, we are in a unique position to demonstrate to the public and other businesses the growing viability and positive environmental and energy-savings benefits of alternate-fuel technologies,” said Walter O’Tormey, vice president, engineering, U.S. Postal Service. O’Tormey spoke to an audience of nearly 100 industry representatives, environmentalists, and Postal Service employees. The hybrid-electric mail-delivery van will be monitored in regular service — delivering mail to Boston-area homes and businesses — to determine its potential for emissions reduction and fuel-economy improvements. It was converted by Azure Dynamics Inc., Boston, a developer of electric and hybrid-electric powertrain systems. Based on the company’s other hybrid applications, and depending on the vehicle and its duty cycle, Azure officials expect fuel-economy improvements to be in the range of 30 to 50 percent. The Postal Service has been testing alternate-fuel vehicles for several years now. In fact, it operates the largest alternative-fuel fleet in the nation — 30,000 vehicles. The fleet includes compressed-natural gas, propane, ethanol, biodiesel, and electric vehicles.