The owner of a downtown Washington restaurant and two others were arrested yesterday after drug agents seized nearly seven pounds of heroin that law enforcement officials said had been smuggled directly from an Iranian heroin processing plant.

Law enforcement authorities said the street value of the drugs was at least $32 million, and described it as perhaps the highest quality and largest quantity of uncut heroin ever seized here. Drug Enforcement Administration agents reportedly had promised a $5 million down payment for the drugs to be delivered to a Southwest Washington bank yesterday, and the arrests were made after the drugs arrived, they said.

The preparation for yesterday's massive deal were orchestrated during dinners and meetings at expensive downtown restaurants, and included earlier law enforcement purchases of about $50,000 worth of heroin from the same suspects at meetings at the Key Bridge Marriott and the upper-level observation deck of Washington National Airport, according to affidavits written by investigators in the case.

Throughout the probe, the undercover DEA agents posed as wealthy prospective drug buyers out of New York, and law enforcement officials said the impression was clearly left with the sellers that the ultimate purchasers were major organized crime figures from that city.

Charged were Mohammed Roshan, of 5500 Friendship Blvd., Chevy Chase, the owner of the West End Restaurant at 915 21st St. NW; Sharokh Michael Bakhtiar, 2001 Somerset St., Hyattsville, identified as a part-time salesman at a Silver Spring car dealership, and Reza Mianegaz, 8339 Garfield Ct., Springfield.

Bakhtiar is an American citizen, and the other two are Iranian nationals, drug agents said.

Federal drug officials said the arrests and seizure are part of a continuing investigation into what they view as an upsurge of Mideast heroin coming into the United States in recent months, and said further arrests are expected in connection with six-month-long investigation here.

A DEA spokesman said undercover agents had made arrangements for the drug purchase recently by flashing what they said was $5 million in a safe-deposit box in the L'Enfant Plaza branch of the National Bank of Washington.

Actually, the drug agents could only arrange to have $1 million in cash available for the seller's perusal, the spokesman said. The seller counted out $500,000 of it by hand and then took the agents' word that the rest was there, the spokesman added.

The sellers "expressed his extreme satisfaction [to the undercover DEA agent] by kissing him," according to affidavits filed in the case.

The three persons arrested yesterday had been the focus of two separate drug investigations several months ago by DEA agents and by D.C. police detectives, sources said. After it was discovered that the two investigations overlapped, they were merged under a continuing DEA-D.C. police drug task force that concentrates on perceived major drug dealers in the Washington area.

Agents also conducted searches at three D.C. area locations yesterday, including Bakhtiar's home and the West End Restaurant. The third location searched was an apartment at 2115 Pennsylvania Ave. NW that had been rented by two unidentified persons involved in the probe, agents said. h

According to the affidavits filed in support of those search warrants, a source informed the DEA that Roshan -- who had allegedly purchased the West End Restaurant for $300,000 -- was a "low-level, high-quality heroin smuggler and distributor . . . during the latter years of the shah's regime" in Iran. The unidentified source also informed the agency about Bakhtiar's alleged involvement in larger drug smuggling schemes, according the affidavit.

Numerous meetings between Bakhtiar and the undercover agent at restaurants along Washington's K Street NW restaurant row and various suburban restaurants are detailed in the affidavits. Bakhtiar reportedly described himself in those meetings as "knowing the people in the laboratory in Iran where the heoin is manufactured," and as having a commercial pilot's license that allowed him to go directly to the source.

After Iranian activits took over the American Embassy in Tehran last November, the undercover DEA agent expressed concern about the political situation in Iran and questioned whether that would cloud the deal, the affidavits said.

Bakhtiar reportedly said "the more confusion in that area the better" for him and the agent. At a later meeting in another well-known Washington restaurant, Bakhtiar reconfirmed, according to the affidavits, "that there would be no problem smuggling heroin out of Iran at this point due to the fact that the authorities there are completely distracted by the political situation."

He reportedly said "his people" were professional Iranian drug smugglers who regularly came into the United States and never had been caught, the affidavits said. DEA agents said the further deal for a larger quantity of heroin then was made, Bakhtiar was shown the money, at the bank, and that he left the county on Dec. 18.

Washington special agent in charge David G. Canady of the drug enforcement administration said last night he believed this was "probably the largest" single heroin seizure in the District of Columbia and that because of its purity the heroin involved could produce three-quarters of a ton of street-purity heroin.

He said the investigation is continuing, and that this seizure "was not just an isolated incident. This is the beginning of the case."

DEA officials said recently they were troubled by an increase in the amount of drugs coming into the U.S. from the "Golden Cresent" of Iran, Afghanistan and Pakistan, the world's largest opium producing area.