It was not until after TWA Flight 840 had landed here yesterday that its crew realized four passengers had been lost.

No one noticed their disappearance in the dust and debris that swirled around the cabin. Adding to the confusion were the screams of those aboard and wind howling through the gaping hole left by the explosion, crew members said at a news conference today.

The blast had come at 2:20 p.m. local time as Flight 840 from Rome was descending at 15,000 feet, 20 minutes from its scheduled landing in Athens. To Capt. Richard Peterson, 55, it sounded like "a shotgun going off next to your ear."

The noise, accompanied by what sounded like breaking glass, made Peterson think at first that a window had exploded in the cockpit. The air instantly filled with dirt and fiberglass insulation, and it was difficult to see. Then he noticed that his door to the passenger compartment, which normally opens outward, had been blown inward.

After a quick check, the flight crew determined that all systems on the aircraft were working. Although he could not see Athens below, Peterson, a veteran of 30 years flying experience, said he knew where it was.

Peterson turned the plane 20 degrees to the left, starting a quick and direct descent while Athens was advised by radio that Flight 840 was heading in for an emergency landing. Over the loudspeaker, he told passengers that they would be landing within 10 minutes and asked them to stay calm.

At least two of the four attendants were new. An ongoing TWA strike has sent numerous new attendants, fresh out of training, to senior overseas routes. Cindy Purdy, of Meadville, Pa., had been on the job for just three weeks. Karen Cavanaugh, 24, of San Diego, had been in the air only 18 days.

Purdy was the crew member nearest the explosion. "I was walking toward the back of the plane from first class," she said, "looking back and forth, to see if there were any cups" lying around. When the explosion came, ahead of her, she grabbed the seat next to her and held on.

"I didn't see anything. There was fog and fiberglass flying everywhere. Pieces of the aircraft had fallen from above," apparently part of the overhead baggage compartment. Then, Purdy saw the hole.

"As soon as I determined I wasn't going to get sucked out, . . . I walked back. I saw the hole below the window, and I thought it was a strange place for a window" to have been blown out. In fact, the hole began just below the window at row 10, gaping down through the floor and about four feet across. Purdy said, "I didn't see anyone leave the aircraft."

Almost immediately, passengers began screaming. At the front of the plane, in first class, chief attendant Catherine Erikson, 30, an Alexandria, Va., native who has been with TWA eight years, said she was "afraid to go back" to row 10, where loose objects in the plane still were being sucked out into the clear blue sky.

The first-class section was crowding with people. In a mindless panic, Erickson said, many had simply grabbed their hand baggage and "fled the scene," running forward and irrationally demanding to be let off the plane.

Erickson and flight attendant Luciano Rodocanachi, a 23-year TWA veteran and Rome resident, pried passengers' locked fingers from around seat backs and dividers and began to work everyone back to a seat.

Oxygen masks had fallen from above, and putting them on -- breathing the clean air rather than the still swirling dust -- seemed to calm many passengers as the attendants moved around fastening seat belts. Erickson said she grabbed some linen napkins from first class and began distributing them to the many passengers whose legs and feet were bleeding from shards of metal and glass.

Erickson and Rodocanachi lifted one woman lying on the floor into a crude jump seat and strapped her in. A family of four Saudi Arabians was found huddled in a three-seat section. Erickson gently pulled apart the husband and wife and seated them separately.

Dennis Taylor, an off-duty TWA pilot who had been riding in first class, became Peterson's "damage control officer," helping to move the injured away from the hole, locating a physician among the passengers to attend to them. Another off-duty TWA crew member riding in the passenger section moved forward and radioed staff on the ground.

Thirteen minutes after the blast, Peterson made what he described as a "normal emergency landing." Then the loss was discovered.