SPRING VALLEY (CNS) - An arson investigation was underway Saturday into the cause of a motor home fire that spread to a Spring Valley strip mall, causing a partial roof collapse while badly damaging a church, authorities said.

While the Full Gospel Church of God in Christ at 545 Grand Ave. sustained major damage estimated at $650,000. Two other businesses in the strip mall had only minor damage, Cal Fire Capt. Brent Pascua said.

The fire ''was not an attack on the church or anything malicious'' and no one was injured in the blaze, which broke out about 9:25 p.m. Friday when a motor home parked on Grand Avenue near Jamacha Boulevard started burning, Pascua said.

About 40 firefighters from several agencies in San Diego, Bonita and El Cajon responded. Downed power lines complicated their efforts, and the fire was not fully knocked down until about 12:45 a.m.,he said.

Services will be held temporarily at the annex at St. Stephen's Cathedral at 5825 Imperial Avenue on Sunday.