The number of bank robberies in the District so far this year is more than double the number for the same time period last year, according to D.C. police, who vowed yesterday to attack the problem aggressively and "curtail the trend."

"There's an old theory that when bank robberies go up, people who are doing time for bank robberies are finishing their sentences in jail and getting out," said D.C. Police Chief Maurice T. Turner. "Whether this theory is true right now, we're going to go after it."

The most recent robbery occurred yesterday about 3 p.m., when a man armed with a silver-colored handgun robbed two tellers at the Columbia First Federal Savings and Loan Association at 5301 Wisconsin Ave. NW, police said. They said it was the third time in the last two months that the branch has been robbed.

Yesterday's holdup raised to 11 the number of robberies of financial institutions in the District since Jan. 1, compared to five at this time last year, police officials said.

The holdup man, who fled with an undetermined amount of money toward the Friendship Heights Metro station, could also be a suspect in at least one other bank robbery, police said.

Deputy Chief Alfonso Gibson, head of the department's criminal investigation division, said that police believe another person may be responsible for at least three other robberies this year.

Turner said the "surge" in bank robberies is "bucking the trend" of other serious crimes in the city, which so far is about 12 percent lower than 1984, he said.

He expressed concern that the number of bank holdups this year could surpass the number last year, when more than 50 financial institutions were robbed, and said that he plans to raise the issue at a staff meeting today.