Another Suit Filed Over Drowning : Woodland Hills: The parents contend that the property from where their son fell lacked a fence and warning signs.

The family of a Woodland Hills teen-ager who drowned in the storm-swollen Los Angeles River has filed a lawsuit alleging that owners of an adjoining property contributed to the tragedy.

The complaint filed by David and Marilyn Bischoff, parents of 15-year-old Adam, alleges that their son fell into the channel from a lot that lacked a fence and warning signs.

The owners of the lot on Ostronic Drive in Woodland Hills, an architect and a construction firm were named as defendants, along with the city of Los Angeles.

The lawsuit, which seeks unspecified damages, was filed Thursday, one day after another wrongful death lawsuit by the Bischoffs against the city and county of Los Angeles, the state, the Los Angeles police and fire departments, the Los Angeles Department of Water and Power, and the U. S. Army Corps of Engineers.

The first lawsuit alleged that the defendants--who operate and maintain the flood-control channel--kept it in a dangerous condition, failed to post warning signs and had no plan for rescuing people who fell into the river.

The victim, an El Camino High School sophomore, fell from his bicycle into the channel during heavy rains Feb. 12, 1992. The 35 m.p.h.-current swept him 10 miles downstream, past dozens of would-be rescuers who threw ropes and dangled from bridges in futile attempts to save him. His body was found the following day, underwater just west of Balboa Boulevard in Encino.

The lawsuit named Brian and Laura Ofria, owners of the Ostronic lot, who could not be reached for comment; architect David Harwell, who said he designed a house for the property but was not involved in any construction; R. B. Gray Construction, and Susmark Development, which could not be reached for comment.

Richard B. Gray, contacted Tuesday, said his firm did not win the job to build a house there.

David Bischoff said that bringing the lawsuits is “very painful for my wife and myself.”

“But the interest we’ve had since very early after Adam died is to make sure that permanent changes are made. Everything acquired from this will be used to further Adam’s name and flood-control safety. I don’t want some child to die 10 years from now.”