HARRISBURG — The number of outpatient surgery centers is continuing to rise rapidly in Pennsylvania, but the growth rate in their profit margins is slowing, according to a new state report.

The total profit margin for all outpatient surgery centers hovered around 21 percent in the 2006 fiscal year, increasing by just two-tenths of a percentage point from 2005.

Since 2001, previous increases had averaged 2.3 percentage points annually, the Pennsylvania Health Care Cost Containment Council said in its report on the finances of those facilities and hospitals that provide specialized medical treatment.

Twenty-eight new outpatient centers opened in the 12 months ended in May, bringing the statewide total to 232 — compared to 174 general acute-care hospitals in the state.

Marc P. Volavka, the agency's executive director, said the council has seen a "significant shift" in diagnostic and surgical procedures performed in the for-profit outpatient surgery centers over the past six years. Those procedures include hemodialysis, chemotherapy, and tooth removal and restoration.

The surgery centers accounted for 28 percent of 2.3 million outpatient procedures performed in the state last year, up from 25 percent in 2005 and 10 percent in 2000.

A statewide lobbying group for hospitals said the increasing competition from the outpatient centers has hurt hospitals' profit margins because the other facilities generally treat healthier people with private health insurance coverage.

"The result is that our community hospitals take in and treat the sickest and most needy patients," Carolyn F. Scanlan, president and chief executive officer of the Hospital & Healthsystem Association of Pennsylvania, said in a statement.

The council found that rehabilitation hospitals had the second-highest average total margins last year, at 13 percent.