Lansdale police are revealing the details about the biggest underage drinking bust in the history of their department.   Thirty-four juveniles were arrested at a party on Pennbrook Parkway after a neighbor complained about the noise on Good Friday.   The five borough police officers that initially arrived on the scene realized they were in over their head and almost immediately called in backup from the surrounding townships.   Investigators say the house was so crowded that the partygoers did not even notice when police officers came inside.