D.C. police surrounded and evacuated an office building at 1909 K St. NW yesterday in a fruitless 2-hour search for three bank robbers who they thought had sought refuge in the seven-story structure. They did not find any of the robbers.

Although the officers came up empty, traffic was disrupted around the building for about an hour, and the occupants of 200 offices and suites in the structure were forced to stand in the mid-day chill for as long as two hours while heavily armed officers combed the building for the wanted men.

Armed with shotguns and wearing blue jump suits, helmets and bullet-proof vests, members of the police Special Operations Division arrived at the building moments after a construction man saw the men believed to be the bandits enter the building.

Police accompanied by K-9 Corps dogs searched all seven office floors and the underground garage for the three men they believed had entered the Riggs National Bank around the corner at 1920 L St. NW about 9:50 a.m. and held up a teller at gunpoint.

No one was hurt in the robbery, but police said two of the bandits were armed with handguns. It was the city's 100th robbery of a financial institution this year, police spokesman Sgt. Joe Gentile said.

Officers said they believed the suspects fled the bank through an alley, then entered 1909 K through a rear entrance. Police recovered a sack of money in the alley leading to the building that the bandits apparently dropped after the bag exploded, spraying red dye. The exploding device had been stuffed among the money by bank personnel. Police did not disclose the amount of money stolen.

Gentile said police believe they recovered most of the money. The three bandits were still at large last night.

Police found two jump suits, two pairs of gloves and two skullcaps, which they believed belonged to the bandits, abandoned in a stairwell between the garage and lobby levels of the building.

At one point, police accosted Al Abney, the building's supervisor of facilities and supplies, believing he was one of the bandits. "They pushed me against a wall and held me at gunpoint until I could identify myself," Abney said. "It shook me up for a while."

Initially, police told workers to stay in their offices. Some stood at windows gaping at the police cars and vans outside and waving to officers, reporters and onlookers. "Send Food," read a sign posted at a window by one group.