A Prince George's County man leaped or fell off the 14th Street bridge early yesterday morning, apparently to his death, after fleeing a U.S. Park police officer making a routine check of cars parked along Hains Point, police said.

D. C. harbor police searched the Potomac River unsuccessfully for the man's body throughout the day yesterday, halting the search when yesterday's cold rain turned to sleet and hail at about 3:30 p.m. Police said the search for the man, identified as Michael S. Magnotto of 28th Parkway in Temple Hills, would resume at daylight today.

Park police reported that Magnotto, 26, was parked at Hains Point with a woman companion at 2:13 a.m. when an officer attempted to make a routine check, since the park area closes at 1:00 a.m. When the officer approached, police said, Magnotto sped off in the 1975 Ford LTD at high speed without turning on his headlights.

The officer, John Monbouquette, told a reporter after the incident that he was only attempting to tell the driver to turn on the lights. But a chase developed as Magnotto sped out of the park and then along the southbound lane of the 14th Street bridge toward Virginia.

Halfway across the bridge, a partially dressed Magnotto suddenly halted the car, darted out and began running north, police said. By then the officer had called for reinforcements. As the additional officers approached, Magnotto climbed the railing and either jumped or fell approximately 40 feet into the frigid Potomac.

Park police said a rescue line was thrown in immediately but Magnotto failed to grasp it. Soon, police said, they lost sight of him.

The woman companion, whom police declined to identify, remained in the car throughout the incident.

A harbor police spokeman said it was possible that Magnotto is still alive, but not likely. "The water's very cold--maybe a little over freezing," the spokesman said. "It doesn't take long before you stiffen up if it's that cold. He may have jumped in and been carried down a ways by the current."

Harbor police joined the search along with a D.C. police helicopter at 2:30 a.m. After a shift change at 4:30 a.m., a second harbor police team dragged the river with weighted hooks until late yesterday afternoon. Police said the river is approximately 25 feet deep and free of ice, but extremely murky.

D.C. police currently list Magnotto as a missing person. If the body is found, the medical examiner will make a determination of the cause of death, police said. Magnotto's behavior continues to puzzle police and relatives who wonder at his volatile reaction to a seemingly routine police traffic check.

"The girl he was with had no motive; she said she didn't know why he did it," said a man reached by telephone who identified himself as Magnotto's father. He said Magnotto had lived with him at 2810 Lumar Drive in Camp Springs until several months ago, but he had not heard from his son in three or four months.

The Prince George's sheriff's office confirmed that Magnotto had been arrested on a narcotics possession and parole violation charge in July but was unable to provide details on the charges or the disposition of the case. Prince George's police spokesman Robert Law said that a check of area and national files indicated no outstanding warrants for Magnotto's arrest.

Police were unable to determine if Magnotto was employed. His companion gave homicide detectives a statement yesterday.

Park police said they have impounded Magnotto's car at their Hains Point headquarters and will obtain a warrant to search it. D. C. police said the vehicle bears Virginia tags but is registered to the Temple Hills address.