Cambridge and state police looked forward to a quick solution of the $50,000 Harvard Cooperative Society robbery yesterday as they announced that they have the names of three as yet unapprehended participants in the January 9 theft.

A fourth man whom police have linked with the holdup, Nicholas Mavrides, is already being held in $60,000 double surety bail, pending trial on an armed robbery charge.

The latest break in the case apparently was the direct consequence of evidence discovered by police in a safe deposit box which they drilled open Wednesday when its owner claimed that he had lost the key. The search warrant permitting this action had been granted by the Newton District Court.

In the box, police found $8,000, plus two manila envelopes containing additional information about the robbery gang. Police declined to elucidate further about the envelopes' contents, but did say that they planned to check the serial numbers of the bills discovered against the numbers of the bills stolen from the Coop.

Box Owner Disappears

While police were counting the money found in the box, a two hour job, the owner did a quick disappearing act. he has not yet been found, and police are withholding his name until they establish a more definite link with the Coop case. A co-holder of the same box could not be reached yesterday.

An additional $7,600 of alleged loot was discovered yesterday when police opened a safe deposit box rented by Mavrides.

In an effort to recover more of the $50,000 loot, detectives assigned to the case plan to search several more safe deposit boxes today.

With these late developments, police became more enthusiastic about the case's progress than they formerly had been. State Detective Daniel I. Murphy declared yesterday that three arrests will be made "in the near future," thanks to several new but as yet unannounced clues which have been discovered.