Elise Andrea Jorgensen, a 77-year-old mother of three, grandmother of 10, and great-grandmother of three, was struck and killed by a passenger train at a pedestrian crossing in Seabrook yesterday as she apparently tried to keep her 7-year-old grandson from harm.

Jorgensen and her grandson Christopher, a perky blond first-grader, were on their way to a 7-Eleven store on Lanham-Severn Road when he ran ahead and crossed the tracks in the path of an oncoming train, according to Prince George's County police and Amtrak.

"The boy tried to cross, succeeded; the woman hesitated, was apparently afraid the child would attempt to return . . . and then, indeed, did cross the tracks," said Clifford Black, an Amtrak spokesman.

Elise Jorgensen was killed shortly before noon by the Amtrak Palmetto, traveling south to Savannah, Ga., from New York at more than 100 miles an hour.

"My grandma died today," Christopher Jorgensen informed a visitor to the family's Seabrook home later yesterday afternoon. "She got hit by the train. First she was there, and then she wasn't."

Black said flashing red lights and a bell were working at the Seabrook Road pedestrian crossing, and that an Amtrak maintenance crew had witnessed the accident.

Prince George's County police spokesman Bruce Gentile said the train's engineer blew the whistle and hit the emergency break but was unable to stop in time.

Elise Jorgensen's son, Ernest Jorgensen Jr., a safety consultant, said yesterday he had worried that the crossing was unsafe, and asked his mother, who had been living with the family since Christmas, to use a bridge slightly further away.

"I know Amtrak has money problems but maybe this will lead them to invest a little money and put in a gate there," he said of the crossing.

Amtrak spokesman Black said he did not know of another accident at the site, which was used as an automobile crossing until 1980, and currently serves as a stop for a commuter train to Washington as well as a pedestrian pathway. Wire fences line the tracks, but a space has been left in them, and a wooden walkway spans the track bed.

Ernest Jorgensen's wife, Hildegard, a registered nurse at Washington Hospital Center, said she did not think the boy had yet fully comprehended what had happened. "I think it will hit him a little later," she said. "He told me, 'Now I will have to stay at the after-school care,' " instead of going home to his grandmother.

Ernest Jorgensen Jr. said his son had come running home after the accident to get help. "He said he didn't see the train until it was too late," Jorgensen said. He said he asked his son if he had looked for his grandmother, and that Christopher replied, "No, because maybe another train will come and hit me."

Hildegard Jorgensen described her mother-in-law as a self-effacing woman, the daughter of a Norwegian sea captain. Elise Jorgensen, she said, had emigrated from Norway and had worked for the telephone company in New York before retiring about 10 years ago. "I just talked the other day at work about she's in such good physical condition, no arthritis, no nothing," she said.

The accident delayed the Palmetto for 1 hour and 13 minutes, and a later train was held up for 10 minutes.