WASHINGTON — The waistlines of America's youths are expanding, shrinking the pool of those eligible to join the U.S. military. But an Army program is giving overweight enlistees a second chance — and helping the military with its own expansion.

The recently introduced waiver program allows enlistees who don't qualify for the military because of their weight a chance to shape up after joining. So far, the program has helped the Army make its recruiting goals in what remains a tight recruiting market.

If the economic recession worsens, it could help the military's recruiting efforts as people seek stable employment. That could reduce the need for waiver programs. However, nutritionists don't see the trend of overweight Americans disappearing any time soon, ensuring the continuance of such programs in recruiting an all-volunteer force.

"We support any service who comes up with a scientifically defensible way of expanding the market (of recruits)," said Curtis Gilroy, director of accessions policy for the Pentagon.

Such waivers had been studied for years, but the program wasn't implemented until fiscal 2007, when it admitted about 1,500 individuals (just a small slice of about 80,000 recruits). Recruits must pass a special battery of tests, including a "step test," and do a number of push-ups to demonstrate their physical abilities. If they pass and are enlisted, they have a year to comply with the Army's physical requirements, measured by "body mass index," a formula that estimates body fat based on weight and height.

The Army's weight waiver program rests largely on a distinction between individuals who are overweight or obese and those who are physically fit but whose "body mass index," or BMI, doesn't meet Army standards.

"The point is to get the football-player kinda kids. It's not to get the couch-potato kids," says Beth Asch, a senior economist at the Rand Corp. who studies military recruiting.

The Army program is a "sensible move," says Asch, but to remain effective it must have oversight.

"There can be a temptation, not necessarily at the commanding level but at the ground level with the recruiter, who would want to slip in a kid who is overweight and has no business being in the Army," she says. "There needs to be monitoring."

So far, the percentage of those in the program who don't get into shape — and are then discharged — is low among both men and women.