Two armed men, dubbed Butch and Sundance by an employe of one of the stores they robbed, are being sought by Northern Virginia police in a series of pharmacy holdups since early May during which cash and a specific list of drugs were taken.

Police said the robberies, at seven drugstores in Fairfax, Arlington and Prince William counties and in Alexandria, apparently involved one or both men, one of whom sometimes wears a wide-brimmed Panama hat.

"It's apparent that the descriptions and methods of operation in all of these robberies are very similar," Lt. A. L. Bratcher of Alexandria said yesterday

The latest robbery was late Thursday afternoon at the Boulevard Drug Center, in the 8000 block of Arlington Boluevard in Fairfax County.

Store manager Terry Watson said the men, whom he described as a pair of "classy looking dudes," one white and one black, hung around the store from 2 to 5:30 "as if they were waiting for a ride or something, until only the clerk and I were left."

Watson said when he bought a drink from the store's soda machine, one of the men even "reached down and got the change for me. . . unbelievable."

About 5:40, Watson said, the men suddenly pulled out long-barreled revolvers. They took cash and morphine-based drugs, then ordered Watson, the clerk and Watson's wife, who had entered the store, to the floor. A witness told police the pair fled in a white Chevrolet with district license tags.

There have been no injuries in the holdups and no sots have been fired, police said. Police estimate the total purcahse value of the drugs taken at about $1,000, but refused to disclose how much cash is missing.

The earlier robberies were at Kessler's Pharmacy, Medical Park Pharmacy, and the Annandale Apothecary, all in Fairfax County, Preston's Pharmacy in Arlington (twice) and the Alexandria Medical Arts Pharmacy (twice).

Prince William County police also are investigating the robbery July 12 of the Woodbridge Pharmacy at Woodbridge and Occoquan roads. Police said two white males were involved, but that the drugs taken and the method of operation were the same.