A man described by law enforcement officials as one of Washington's "most notorious and flagrant streetlevel narcotics dealer" was sentenced to 30 to 90 years in prison yesterday and fined $50,000.

John R. (Stampede) Johnson, 36, who has been jailed since his arrest on drug charged last fall, also must serve four years for past convictions, according to the sentence imposed by U.S. District Judge George L. Hart Jr.

Johnson was convicted about a month ago on the basis of an extensive investigation by a joint D.C. Police Department-U.S. Drug Enforcement Administration task force aimed at midlevel and higher D.C. are drug dealers.

As part of the investigation, the task force made extensive use of undercover agents and informants, but added another, more unusual element of surveillance - videotapes of Johnson's alleged drug ring in operation at 7th and T streets NW.

The tapes showed nearly empty streets at the beginning of a day that soon turned into a virtual sidewalk "drug store" that busily sold thousands of dollars worth of illegal drugs daily.

It even provided curbside service to drivers, selling the drugs through car windows after packages were retrieved from various hiding places - including a hollow trees - along the street.