Rescue teams and divers launched a search this morning for a rowing coach who reportedly went into the Potomac River south of Reagan National Airport while coaching novice rowers in a summer crew program.

The missing man was identified as John Steve Catilo, 20, a senior at the University of Virginia who was volunteering as a coach for Alexandria's crew boosters' summer program, which teaches rowing to teenagers and adults from all over the region. Catilo graduated from T.C. Williams High School in Alexandria and had eight years experience as a rower and coach of the summer program.

Teams from the Alexandria and Washington, D.C., fire departments and the D.C. Harbor Police rushed to the scene near the Daingerfield Island sailing marina shortly after an 8:59 a.m. call that the coach had gone under the water, said Jane Malik, a spokeswoman for the Alexandria Fire Department.

"At this point they sent divers in to look for a body," Malik said.

Catilo was coaching one of two novice boats with nine students in it when he fell out of his separate chase boat, a launch with a small outboard motor, authorities said.

Around 3 p.m. officials stopped the search because the tide was shifting under the water making it difficult for divers to continue, according to Lt. Alfred Durham, a spokesman for the Harbor Patrol's special division operation. The search will resume Saturday morning at 5:30 a.m., he said.

Durham said the problems began this morning when the missing coach's boat apparently stalled. "When he stood up to restart it, he lost his balance and ended up in the river," Durham said. "He fell overboard."

Catilo was not wearing a life vest, Durham told reporters earlier today.

"If the victim had been wearing a PFD [personal flotation device], we wouldn't be standing here now," Durham said at vantage point near the scene.

He said the Harbor Police had seven divers searching for the coach. The divers concentrated on an area of the river determined from witnesses and the U.S. Coast Guard, which provided a model of where to look based on the tide and wind. The site is in the channel of the Potomac about 100 to 200 yards offshore.

D.C. authorities are handling the investigation since the accident happened in the District's jurisdiction, officials said.

A U.S. Park Police helicopter and a D.C. fire boat also assisted in the search, Malik said.

The Alexandria Fire Department's water rescue team includes two inflatable boats and a hard-hulled boat. The sailing marina is off the George Washington Memorial Parkway south of the airport.