D.C. police detectives were increasingly skeptical yesterday about a motorist's report that a woman threw a baby 40 feet off the John Philip Sousa Bridge Tuesday afternoon and then dived into the Anacostia River.

Harbor police dredged the river yesterday morning in search of the woman and child, whose identities were not known. The search was suspended by noon because of the snowy weather, police said.

Police sources said that they were puzzled by the man's story because, despite heavy traffic on the bridge at the time, no other witnesses called police to report it.

Police have not received a call from one purported witness, a driver who the motorist claimed was behind his car when the woman allegedly jumped. Three workers on the western bank of the bridge about 75 yards away told police they did not see the incident, police said.

Police said the motorist did not stop on the bridge. He apparently drove about eight blocks away to his home on S Street SE before calling police, instead of calling from a pay phone or business closer to the bridge, they said.

The motorist, a 32-year-old security guard who works at a nursing home at 3333 Wisconsin Ave. NW,, told police Tuesday that he picked up a hitchhiking woman with an infant about 1:45 p.m. at a McDonald's restaurant at Barney Circle and Pennsylvania Avenue SE near the bridge, a police spokesman said.

The motorist told police that he picked up the woman and child because he was concerned that the infant was not properly dressed for the chilly weather. The motorist told police that as he drove southeast on Pennsylvania Avenue over the bridge, the woman became agitated and asked him to let her out of the car.

When he refused to stop the car, police said, the woman struck him with her hand, causing him to slow to nearly a stop. The woman then jumped from the car, went over to the guardrail, threw the infant into the river and then jumped in, the motorist told police.

Capt. William White III said Tuesday that police had determined that the motorist was reliable after calling his employer, International Security Corp., and talking to one of his relatives.

But doubts grew yesterday as police failed to corroborate the man's account. "It seems like more than one person should have seen the incident," a police source said.