Great America amusement park has decided to require all its employees to undergo drug testing because of a growing problem in the area, a spokeswoman said. The new policy will require drug testing for the Santa Clara theme park’s 150 full-time, year-round workers and all its job applicants. It may be expanded to include its 2,500 summer workers. Any full-time employee who tests positive for illegal drugs or who has been drinking on the job can be fired for the first offense. “Its intention is to keep the work force alert and productive,” spokeswoman Lisa Lovell said. She said there has been no specific drug problem in the park.