Can an employer not hire me for a temporary job position because I will be leaving for boot camp soon?

I'm in the NAVY DEP (Delayed Entry Program) and will be leaving for boot camp August 12, 2009. I enquired about a second job; the job is a temporary lawn maintence job for the city and ends November 1, 2009. At the interview they asked me If I would be going on any vacations soon so I mentioned that I would be going to boot camp in August and they informed me that they need someone to be able to work the til november not just til August and good luck finding another job. Is that legal?