By Joan Gralla June 16 (Reuters) - Job-hunting teenagers in cities across the United States face the third bleak summer in a row. They must compete for scarce slots in scaled-back government work programs and against adults forced into low-paying positions by the unemployment crisis. The harsh summer job market for teens is compounded by this: The country has recovered only half the jobs lost from December 2007 through June 2009, the worst recession in 70 years.