Washington police investigators yesterday morning found a third kilo of heroin, with a street value of $7 million, hidden in the apartment of a slain gas station manager, narcotics detectives said.

The find brings the total value of the drugs uncovered in the apartment to $22.4 million, the largest seizure of pure heroin in the police department's history. Detectives discovered 4 pounds 13 ounces of pure heroin in the apartment Thursday morning. Yesterday's additional find weighed 2 pounds 2 ounces.

Narcotics detective Ira Heane spotted an envelope containing the heroin in a gap in a kitchen wall 20 minutes after he began a follow-up search of the basement apartment at 1929 Calvert St. NW, where the body of Rasheed K. Zaman, 34, was found Thursday with a bullet wound to the head.

Police said they didn't find the envelope Thursday because their investigation was cut short when the fumes of fingerprinting chemicals filled the apartment and detectives began choking.

Heane said that the heroin found yesterday was inside a grayish envelope above some kitchen cabinets, just below the ceiling.

Capt. James Nestor said investigators are mystified both by the enormous amount of heroin found in the apartment and the questions remaining about Zaman's connection to the drug trade here.

"Where does he fit in the drug trade in Washington? Were the drugs for distribution in D.C.? That's what we're trying to figure out," Nestor said yesterday.

He said that Zaman, who told his boss at the Rock Creek Gulf gas station that he had to visit his mother in Pakistan last March, "may have been sitting on that stuff because he was a novice and didn't know what to do with it. Or he may have been affiliated with one of those tribes that grows it opium , for all we know."

Police said that there may be a "serious" heroin shortage and a subsequent jump in prices in the District's drug market if the heroin they have uncovered had been intended for distribution here.

Narcotics experts said that D.C. is swarming with "independent" drug traffickers. "There is no way to tell how many there are out there," one expert said. And officials acknowledge that the big pushers rarely are caught.

"There'll be another shipment in soon," a narcotics expert said. "Finding $22.4 million means that we've got a real serious problem here. It's an epidemic. The number of junkies is growing. The number of young people being exposed to drugs is growing."

Officials estimate that there are as many as 15,000 heroin addicts in the city.

Police speculate that Zaman may have been killed by a would-be robber or burglar, but say that they have no suspects in his death.