An Iranian recently arrested on drug charges in this state fled the United States Tuesday with the knowledge of the Immigration and Naturalization Service and the Rhode Island Attorney General's department. Nothing was done to prevent the escape.

The Iranian's brother, also facing drug charges here, is planning to leave the country Saturday night, according to an INS official, and no steps are being taken to detain him.

It is unclear whether the uncontested departures are intended to avoid worsening the tense situation between the United States and Iran or are a result of bureaucratic confusion.

Seyed Gholan Marzarei, 26, and Mohammad Reza Marzarei, 24, were arrested last Friday in a second-floor apartment they shared behind the post office in the village of Wakefield. They were charged with possession of marijuana and morphine and released when they made bail of $5,500 each.

A roommate of the brothers an Iranian named Samad Karbasi, is currently in a state correction institution awaiting trail on other drug charges involving a September seizure of herion. State and narcotics officials said their analysis showed the heroin to be 98.2 percent pure and called it perhaps the purest ever found in the United States.

Leo Gracik, chief of the Rhode Island Division of Drug Control, put the heroin's value at $1 million and said characteristics, including grayish color, suggest that it came for Iran.

Director Frank P. Castelnovo of the U.S. immigration office said the two brothers appeared there Monday, said they intended to return to Iran, and displayed airline tickets for the trip.

Castelnovo said that, before the drug charges were brought, his office was preparing to deport the Iranians because they were in the country illegally.

After seeing the airplane tickets, he said, one of his agents immediately alerted state officials. He said his own agency immediately alerted state officials. He said his own agency had no authority to hold the Iranians.

Allen P. Rubine, assistant state attorney general, said his department decided to defer to immigration authorities and do nothing to stop the departures. Gracik, the drug control chief, said he expressed no objection to the department because of the "international situtation."