A District man yesterday was convicted of narcotics charges in a rare instance in which prosecutors used the defendant's fingerprints on plastic bags containing heroin, rather than actual observations of him selling the drug, as its chief evidence in court.

Ernest L. Hooks, 27, of 1621 Hobart St. NW, faces up to 65 years in prison following his conviction in D.C. Superior Court on two counts of heroin possession with intent to distribute.

Hooks, who has previous convictions on narcotics and weapons charges, was implicated in the case after police, using a secret observation post, seized more than 70 packages of heroin from two other men in drug busts two years ago.

Hooks was not immediately charged because he was not observed participating in any drug transactions. However, authorities said they believed Hooks was behind the deals and later matched his fingerprints with those found on plastic bags seized during arrests.

Another man pleaded guilty to heroin possession earlier this week in connection with the case.

An attorney for Hooks told jurors that federal prosecutors had failed to prove his client's involvement because they could not show that Hooks' handling of the bags had anything to do with their use as containers for drugs.

Assistant U.S. Attorney Tom Roberts said it was the first time the fingerprint tactic had been used in court here. Typically, prosecutors rely on police observations of drug sales, as well as seized drugs, as their chief evidence in narcotics cases.

Judge Tim Murphy set sentencing for Sept. 22.