The Bank of Bethesda branch in the Westwood Shopping Center may have thought its bank robbery problems were solved yesterday when a District man was sentenced by a Montgomery County Circuit Court judge to 30 years in prison for robbing the financial institution Jan. 11.

But slightly more than an hour after that sentencing, the bank was robbed again--by two men whom county police have not caught.

According to county police, yesterday's robbery occurred when two men armed with handguns entered the bank and ordered customers and employes to the rear of the building. One of the suspects removed an undisclosed sum of money from the cash drawers while his companion kept a gun trained on customers and employes. They fled by car and as of late yesterday afternoon police were still searching for the pair.

An hour earlier, Judge John Mitchell sentenced Michael J. Wilson-Bey, 32, of 11th Street NW, to 30 years for the Jan. 11 robbery. Wilson-Bey pleaded guilty last month to armed robbery, theft, two robbery charges, five assault charges and assault on a police officer while resisting arrest.

Wilson-Bey was captured by police the day of the robbery after a wild, block-long chase.

Police had been staking out the bank in response to a rash of robberies. The bank was robbed twice last December. Until yesterday morning, it had not been robbed since Wilson-Bey was arrested. Another Washington man, now being held in the county jail, is scheduled to stand trial Dec. 30 for one of the earlier robberies.