Sgt. Edward Dory, the stocky no-nonsense chief of the metropolitant police robbery squad, was investigating an earlier bank robbery when he heard the word over his police radio: the city's 18th bank robbery for the month of August has just taken place.

The circumstances were fairly typical. Two gun-toting robbers had walked into the bank, Northwestern Federal Savings and Loan Association at 119 Carroll St. NW, and, while one held a gun to the bank's assistant manager, the other ransacked the teller's counter collecting money.

No one was hurt and an undisclosed amount of money was taken.It was significant nonetheless. More banks were robbed in the city last month than in any other month in the last two years.

A year ago, only three bank robberies occurred during August. Last week alone a record number of eight robberies occurred, sometimes two and three being committed in a single day. Most have been committed in the downtown business district and have occurred during times of heavy pedestrian traffic, enabling robbers to mix undistinguishable in the crowds.

"It's the first time I recall that many robberies in a week," said Dory, a 21-year veteran of the D.C. police force.

"It seemed like we have barely enough time to do the preliminaries, interviewing witnesses and so forth, when it was time to go out on another one," he said. "We knew something was brewing up because before Aug. 21 the robberies became more frequent. It seemed like last week became the boiling point. But why that many have occurred is anyone's guess."

Joseph Corless, assistant special agent in charge and head of the criminal division of the Washington field office of the FBI said, "It's hard to attach any certain reason for the high number of robberies we've had this month. We don't know why, frankly." Corless's bank robbery squad works jointly with the D.C. police in all bank robbery cases, which are federal offenses.

A spokesman for the D.C. Bankers Association, Warren Love, said bankers place much of the blame on the courts for bank robberies. He feels the courts give sentences that are too lenient for the crime.

"So many of these criminals already have a record and are on probation for other offenses when they rob banks," said Love, chairman of the association's protective committee and a senior vice president of the Security National Bank. "Judges too often let the criminal off with what amounts to a slap on the hand, and then they are back on the street."

Bank robbers can get up to 25 years for a bank robbery conviction, said Charles Roistacher, assistant U.S. attorney and chief of the grand jury section. "I've seen cases where they have gotten probation and I've seen cases where they've gotten up to 20 years," he said. "You cannot expect any certain sentence. Without a doubt bank robberies are a serious problem. Robbers are terrorizing the banks."

According to statistics provided by the administration office of the U.S. District Court, of the 40 persons sentenced for bank robbery last year in the District of Columbia, 33 went to jail with average sentences of about eight years, while seven received probation.

Dory, of the D.C. Police Robbery Squad, said those sentenced usually serve only three years, which is about one-third of their terms before going on parole. While no figures are available on the number of parolees committed bank robberies, Dory said he estimates that about 30 percent will rob banks again, though not necessarily in the same area.

"Bank robbers in the District are not the kind that you see in the movies," Dory said. "A robber is usually a male between the ages of 18 to 25, unemployed without a skill or trade, usually has other juvenile or adult criminal offenses.

"Because tellers seldom keep more than $2,000 in the cages, robbers usually don't get much - just enough money to buy a couple pair of shoes, or suits, give a little change money to friends and then the money is all gone. That's when the go out and start doing it all over again.

Love, of the bankers association, said District of Columbia banks conform to U.S. banking security regulations and that Treasury Department bank examiners check periodically to make sure banks follow regulations. "But we can't make banks fortresses," he added. "If you build a barricade, how can the customers get service?"

Banks use a variety of security precautions, ranging from guards and bullet-resistant glass for tellers' cages to explosive dye bags that mark robbers, to surveillance cameras - considered by law enforcement officials as the most effective tool in catching criminals.

D.C. police said the success rate in solving cases is about 90 percent while the FBI estimates the solution rate, based on slightly different criteria, to be about 80 percent. Statistics showing conviction rates are unavailable, police said, because often a robber who has committed several robberies before being caught will plea bargain, resulting in some charges being dropped.

Douglas R. Smith, chairman of the board of National Savings and Trust company, which saw three of its branches robbed in a two-week period, said, "Our gravest concern is what this is doing to our personnel. "We've had to reassign people who don't feel comfortable in that position, and in some cases, women have resigned because of the hazards."