Winston B. Prude and Lee R. Heinsch were roommates at the University of New Mexico in the early 1970s. Prude became a lawyer in the District of Columbia, Heinsch an archeologist in Albuquerque.

Early this year, Prude phoned Heinsch, asking him to purchase some heroin for him, Heinsch said in a statement submitted here yesterday in U.S. District Court. At first, Heinsch refused. But when Prude repeated the request in April and sent $290 in cash by overnight courier, Heinsch said he bought the heroin and sent it to Prude by Express Mail.

Three days later, Prude was found dead from a heroin overdose in his Capitol Hill apartment. Police said they traced the drug back to Heinsch.

Heinsch pleaded guilty yesterday to distribution of heroin and using the mails for unlawful activity.

His lawyer, William W. Taylor III, told Judge Barrington D. Parker that Heinsch sent the heroin as "a favor" and included a note with the drug warning that the heroin was "very pure and should be used carefully."

Heinsch's statement, confirmed by federal prosecutors, said the Express Mail package also contained several dollars in change from the purchase.

"It was not a transaction for profit," Taylor said. "He Heinsch was as distressed about Prude's death as we all were."

Heinsch, 33, faces up to 20 years in jail and fines of up to $135,000. Parker allowed him to remain free on $50,000 bond until sentencing on Jan. 7.

Before his death, Prude, 34, was a Justice Department lawyer for four years and then practiced law for two years.

Prude was arrested in May 1983 along with Eric M. Breindel, then a Senate Intelligence Committee staff member, when attempting to buy heroin from an undercover police officer. Both men pleaded guilty to a misdemeanor charge of drug possession and were each sentenced to one year's probation.