An Alpha Beta supermarket in Santa Rosa is taking no chances with an anonymous telephoned warning this week that the store's turkeys had been tampered with, officials said. The store, one of two Alpha Betas in the Northern California city, issued an alert asking customers who bought their birds before Tuesday afternoon to return them for free replacements. The store, which declined to provide details on the threat, also cleared its shelves of the remaining birds. Police are investigating, and the state's food and drug testing facility in Berkeley was testing turkeys from the store. No contamination has been reported.