American Health Services Corp. reported a loss of $665,000 for the third quarter. It had a loss of $708,000 for the comparable quarter in 1987. Revenue more than doubled, to $3.9 million from $1.5 million last year. The increased revenue reflects the addition of new medical centers opened at the end of 1987. The Stop Smoking Clinics business acquired by the company in the first half of 1988 contributed $226,000 of revenue, the company said. A final provision for loss on disposal of assets of $256,000 and a $512,000 investment in research and development resulted in the loss, the company said. The Newport Beach company reported a net loss for the 9 months of $1.8 million. It had net loss of $2.7 million a year earlier. Revenue for the 9 months climbed to $11.2 million from $4.2 million recorded for the like period a year ago. American Health Services’ core business is the establishment and operation of diagnostic-treatment centers affiliated with hospitals, health maintenance organizations, multispecialty clinics and physician group practices.