Challenged by the biggest jewel robbery in the city in 29 years, Newark police last night were digging for clews that would lead them to the three armed bandits who yesterday robbed the Wiss Sons, Inc., jewelry store at 665 Broad street of $50,000 worth of diamonds.

A teletype alarm issued by Newark police headquarters described the three bandits as between 40 and 50 years of age, about 5 feet 8 inches in height and weighing between 175 pounds and 200 pounds.

An automobile, which may have been used by the bandits, was spotted parked in Division street near Spring street last night by Detective Hueber, riding with Sergeant Duhig's roving squad. The car, reported stolen yesterday morning by John J. Fullam of 1715 Boulevard, North Bergen, in that city, was towed to the police garage for examination.

Store employees said one of the bandits stood near the door during the holdup and that one of the other two went behind Rose's counter to the trays of diamonds. After the stones were taken the three men backed out the door as the burglar alarm sounded and then ran across Broad street and through Military Park, according to employees.

No getaway car was seen. One member of the sales force said the trio disappeared behind the Wars of America monument in the park.

A woman employee who declined to give her name said she looked up as the three men entered and saw them holding handkerchiefs over their faces. She said she thought at first "gas was escaping somewhere," but the men drew guns and one announced the stickup.

Police Early at Scene

Police were on the scene almost immediately after the alarm sounded, covering both the Broad street and West Park street entrances to the store. The bandits, however, had made their getaway.

There were no customers in the store at the time.

Another employee said the three men apparently knew that trays of diamonds were taken from the safe at 9:15 A.M. and then taken to showcases. When the men entered, she said, distribution of the diamonds was not finished. This employee said she thought the bandits appeared at 9:20 A.M.

One or more of the bandits was thought to have touched the center counter. Police dusted it in search of fingerprints.

The bandits ignored diamond rings, pins, bracelets and the like on display at Rose's counter and gave their attention only to the loose stones.

Employees were unable to give complete descriptions of the three men. One eyewitness, however, said all three were white men and well dressed.

The Wiss store is one of Newark's oldest and will mark its 106th anniversary in May. It was founded by Jacob Wiss, a Swiss immigrant, who opened a modest cutlery business in 1848.