American Health Services said it lost $708,516 in the third quarter, compared with a loss of $261,672 in the year-earlier period. Revenues for the quarter increased 39%, to $1.5 million from $1.1 million in 1986. The Newport Beach operator of outpatient diagnostic centers attributed this year's loss primarily to a planned investment of $502,298 for research and development associated with a new therapy for treating chronic pain and nicotine withdrawal. For the first nine months of the year, the company lost $2.7 million, compared with a loss of $934,225 last year. Revenues for the nine months increased 57%, to $4.2 million from $2.7 million for the same period last year. Through joint ventures with hospitals, American Health is building a national network of outpatient centers offering diagnostic services in general radiology, magnetic resonance imaging, cardiology and neurosciences.