The Allen Telescope Array (ATA) is a multiuser instrument and will perform simultaneous radio astronomy and radio search for extraterrestrial intelligence (SETI) observations. It is a multibeam instrument, with 16 independently steerable dual-polarization beams at four different tunings. Here we describe a new method for identifying radio frequency interference (RFI) that leverages the unique attributes of the ATA. Given four beams at one tuning, it is possible to distinguish RFI from true ETI signals by pointing the beams in different directions. Any signal that appears in more than one beam can be identified as RFI and ignored. We discuss the effectiveness of this approach using realistic simulations of the fully populated 350 element configuration of the ATA as well as the interim 32 element configuration. Over a 5 min integration period, we find RFI rejection ratios exceeding 50 dB over most of the sky.