Cocaine and heroin with a street value of about $2 million were seized last night by D.C. police at a Southwest Washington apartment after the drugs were discovered by maintenance personnel investigating a report of a water leak, police officials reported.

The more than seven pounds of uncut, or very pure, cocaine confiscated was believed to be the largest amount of cocaine ever seized in the District.

They said 750 small packets of cocaine that were ready for street sale and drug-processing equipment were confiscated from a fifth-floor apartment at 4660 Martin Luther King Ave. SW, and that it appeared the apartment was being used as a narcotics laboratory and the center of a major drug distribution business.

Seventh District Sgts. Winslow McGill and Leon Swain, who led the police raid, estimated the street value for the cocaine at more than $800,000.

A quarter-pound of uncut heroin, with an estimated street value of more than $1 million, was also found in the apartment, police said.

A late-model BMW 320i automobile with D.C. license plates that police said are registered to an Oldsmobile alsowas seized outside the building, police said.

A total of $2,700 in cash, mostly in $100 bills, and a telephone pager also were seized, police said.

Two men were arrested at the apartment building and each was charged with violating the federal Uniform Controlled Substance Act for possession with intent to distribute cocaine and heroin, according to a police.

They identified the men as Larry Blackwell, 35, of 11907 Autumn Wood La., Fort Washington, and Torrence D. Owens, 36, of 210 Seventh St. SE.

Both men were being held last night in the central cell block at D.C. police headquarters pending arraignment today in U.S. District Court.

Police said the seizure grew from "purely coincidental" circumstances.

They said the drug cache was discovered by workmen who went to the two-bedroom apartment after a tenant who lives in an apartment one floor below complained that water was leaking through the ceiling.

When the workmen arrived, police said, they found a leak in the kitchen and a large quantity of drugs and drug paraphernalia in the apartment that was almost devoid of furniture and other personal belongings.

The workmen reported their discovery to the apartment management, and the management then notified police.

Based on the information provided about the contents of the apartment, police secured a search warrant from a D.C. Superior Court judge and arrived at the apartment about 5:30 p.m., officials said.

Police said the apartment was apparently the center of a major drug operation.

In addition to the narcotics, police said officers from the 7th District vice squad seized scales, substances used to "cut," or mix with the drugs face masks and a machine used to press large quantities of narcotics into bricks.

"The whole place was set up just for dealing drugs," a narcotics detective said early today. "There's no question it was a big-time operation."

Police said field tests on the drugs were conducted at the apartment and the results showed the substances to be cocaine and heroin.

Narcotics officers said that an ounce of pure cocaine sells for about $5,000. Cocaine sold on the street brings an estimated $100 to $125 per gram.

Heroin is usually sold on the street at a purity of about 5 percent and a small amount, called a "quarter" and containing 250 milligrams of the diluted drug, sells for about $25 to $40.

Police said that as several officers were leaving the apartment, they noticed two men walking toward them down a hallway, and that both men turned and fled.

One of the men was captured immediately and the other was taken into custody on the fourth floor, police said.

They said that neither man is the person listed as the tenant on the lease for the apartment, located in a high-rise building near Hadley Memorial Hospital in far Southwest.