Five persons were arrested in Arlington early yesterday on drug charges after what was described as a 2 1/2-month investigation, county police reported.

County drug investigators, working with the Washington field office of the federal Drug Enforcement Administration, said they made the arrests about 1:40 a.m. in an Arlington motel room at an undisclosed location. Police said the arrests came after investigators arranged to make a purchase of about one kilogram of cocaine.

Police said they confiscated more than three pounds of cocaine that they said had a street value estimated at more than $750,000. Police also seized guns, what they described as drug paraphernalia, and a large sum of money. No further details of the arrests and reported confiscations were available.

Police said they arrested Lionel Giron, age unknown, of the 2000 block of N. Scott Street in Arlington, and Shahram Nadjafi, 20, whom they listed as living in the 4000 block of Hummer Road in Annandale, and charged both with distribution of cocaine.

Gregorio Seijf, with no known age or fixed address, was arrested and charged with possession of cocaine with the intent to distribute, police said. Teresa Perez, 35, and Oscar Dominguez, 22, both of the 2600 block of Lee Highway in Arlington, also were arrested and charged with possession of cocaine with intent to distribute, police said.