Massachusetts veterans and their dependents appear to be losing hundreds of thousands of dollars in annual state benefits because the municipal officials who serve veterans are unaware of available aid, not working state-mandated hours, or do not try hard enough to find veterans in their communities, state officials say. As a result, officials believe, thousands of eligible veterans might not be receiving cash payments and medical reimbursements at a critical time, when the economy is poor and Iraq and Afghanistan veterans are joining the ranks of elderly and graying counterparts from World War II to Vietnam. .