Samuel Franks, 65, of Chevy Chase, was stabbed to death yesterday in the small jewelry store he had operated for eight years at 1406 K St. NW., during an apparent robbery, police said.

Detectives had only sketchy reports of what had happened and what might have been stolen. There apparently was no witnesses to the crime.

But the investigators said the interior obviously had been ransacked and that empty cases that had held items on display were strewn about the premises. But the robber or robbers, their movements apparently quickened by the knowledge that Frank's body might be discovered by a customer at any moment, left watches, rings, earings and other items still on their display stands in the jewelry and watch-repair shop.

Franks, who investigators said came to this country from England about 40 years ago, was found behind the counter of the shop by a doorman from the adjacent Ambassador Hotel about 2:25 p.m., apparently only minutes after the attack had occurred.

Franks normally closed at about 2 p.m. on Mondays, a fact that led detectives to theorize that he already had locked up in the shop's safe most of the more valuable items in his inventory.

"A lady came by asking about him, saying that she had looked in and nobody was there," said William Thomas, the Ambassador doorman who discovered the body.

Thomas said that before he entered the small store, he thought that Franks had closed for the day. But then, he said, "I looked over the display counters and he was lying there. I yelled Franks, Franks. I thought he had had a heart attack."

Thomas said he did not know that Franks had been murdered until after police told him.

Franks had asked Thomas and other doorman "to keep an eye on the shop, especially when his wife worked there," Thomas said. Franks usually worked in the store alone.

Thomas and others in the area said Franks usually opened the store about 8 a.m. and closed in early afternoon.

Ted Dividov, manager of the Ambassador drug store, which is along side the jewelry store, recalled that Franks had purchased the store from a man who sold out after he had been tied up and gagged during a robbery some years ago at the shop.

Ahmad Manna, manager of a nearby carry-out, knew Franks well. Almost daily, he said, the jeweler would bring his lunch to be kept in the restaurant refrigerator, Manna said.

Yesterday Frank's lunch was still there - a pear, a tomato, a sandwich, orange juice and a soft drink.

Franks' murder was the 13th homicide in the city this year.