County police apparently cut off the beer supply to a party Friday night when they stopped two teen-agers and found two-and-a-half cases of beer behind the passenger seat of the car.

The youths, 16 and 15, were issued juvenile citations for unlawful possession of alcohol, county police said yesterday.

An officer on a detail enforcing alcohol violations said he noticed youths in a car on the parking lot at Goldberg's Liquors, Ritchie Highway and 14th Avenue, followed the car when it drove off and stopped the vehicle on a speeding violation.

The officer said the teens told him they were taking the beer to a party in Pasadena.