Francis E. Brazell, 29, has been charged by police with operating an Internet escort service employing underage girls.  The Philadelphia man was arraigned yesterday on charges of prostitution and related offenses, criminal conspiracy and corruption of minors.  An investigation into area escort services led authorities to Robin's Nest Escort Service.  They advertise the services of male and female escorts, claiming all the escorts are of legal age, on a Web site.  Two undercover state troopers called the service April 12th, and were directed to it Web site  A meeting was set up and when the girls showed up at the hotel room at the appointed hour they agreed to joint oral sex for money.  Two girls arrived from the escort service at the officers' hotel room at the Marriott West Hotel in Montgomery County at 10 p.m. Friday and immediately agreed to perform oral sex on the troopers in exchanged for $500.  After they were arrested the women told the troopers they were each 17 years old and worked for Brazell who is given part of their earnings.  Brazell was arrested by officers around 11:30 p.m. when he arrived to pick up the girls.  The teenage girls, whose identities are being withheld because they are minors, were charged with prostitution.  They will be tried as juveniles.  Brazell faces a maximum of seven years in prison if convicted.  The Web site has been removed from the Internet.