An AA is a good start. The choice of a major is not nearly as important as the college experience itself. The best predictor of future behavior is past performance. Positive job references from a reputable employer are extremely important. Any consistent employment is helpful, however jobs which emphasize public contact, interpersonal communications, dependability and responsibility are the most important.
Most agencies have part-time positions.
They may be cadets, community service officers, police aides, public safety aides, etc. All provide exposure to the law enforcement environment. Agencies also have volunteer programs that can provide similar exposure and may also lead to employment opportunities. Start now on an ongoing physical fitness program, since you will need to be in good physical condition to successfully compete for employment and complete a police academy. While perfection is not expected or required, drug use, theft, dishonesty and poor judgment end many careers before they get started.