One of three men accused of plotting to import about $32 million worth of high-grade heroin from Iran to the United States pleaded guilty yesterday to two racketeering charges related to the case.

Riza Mianegaz, an Iranian citizen living in Springfield has also agreed to cooperate with federal drug agents to their continuing investigation into the recent influx of Mideast heroin into the United States, according to documents filed in U.S. District Court in Alexandria.

Mianegaz and two others, Mohammed Roshan, operator of the West End Restaurant in downtown Washington, and Shahrokh Michael Bakhtiar of Hyattsville, were arrested Feb. 6 after drug agents seized nearly seven pounds of heroin that authorities said had been smuggled directly from an Iranian heroin processing plant.

Law enforcement officials described the seizure as perhaps the highest quality and largest quantity of uncut heroin ever confiscsted here. Undercover Drug Enforcement Administration agents had displayed what they said was $5 million in a safe-deposit box at a Southwest Washington bank, and the arrests were made shortly after the drugs arrived, authorities said.

Bakhtiar, identified as the alleged ringleader, and Roshan also appeared in federal court yesterday for a pretrial hearing into an attempt by their attorneys to suppress evidence gathered during the probe.

Judge Albert V. Bryan Jr. scheduled final arguments on the defense motions for Monday after listening to more than 2 1/2 hours of testimony.

Earlier, at an unscheduled morning hearing, Mianegaz pleaded guilty to charges of twice furnishing heroin to Bakhtiar that Bakhtiar then allegedly sold to undercover agents in purchases that led to the Feb. 6 deal.

Sentencing for Mianegaz is scheduled for April 18.