A gunman held up a National Bank of Washington branch in Far Southeast just before it opened yesterday and escaped with about $70,000.

Police said it was the biggest haul in a bank robbery in the city this year, but that the bandit -- who obviously had planned the holdup carefully -- missed another $50,000 that had been within his reach.

The robbery was the 82nd this year of a District financial institution compared with last year's total of 55.

Police theorized the increase was linked to the recent upswing in drugs trafficking, which created a greater need for cash among users, as well as a flow of holdup men released from prison after serving their terms who have reverted to crime.

The gunman yesterday forced his way into the NBW branch at 2844 Alabama Ave. SE at about 8:30 a.m. by surprising a female employe and putting a shotgun to her back. Once inside, he ordered 10 employes to lie on the floor, investigators said.

Police said he then ordered bank security guard Dan Williams to open the vault, but found that the bank's metal cash boxes already had been removed in preparation for the 9 a.m. opening. The gunman then ordered Perry Cheek, 27, the assistant manager, to empty the contents of the boxes into a leather bag. The robber made off with cash from four boxes, but ignored a fifth that contained $50,000, bank officials told police.

Sgt. Edward Dory, chief of the city bank squad, said the robber was one of the best prepared his squad had encountered.

"He knew just what to do and when to do it," Dory said. "It was no run-of-the-mill bank robbery."

Dory said the robber knew which of the employes was the last scheduled to enter the branch. By robbing the bank before hours, the man did not have to be concerned about bank cameras and tellers' silent alarms because cameras had not been activated and tellers were not yet at their posts, police said.