U.S. Customs agents seized 1 1/2 pounds of heroin worth an estimated $1 million Saturday from the luggage of a Hyattsville resident arriving at Dulles International Airport, a Customs spokesman said yesterday.

The heroin was found in a cigarette carton from which the cigarettes had been removed, the spokesman said, adding that it was the largest heroin seizure at Dulles since 1974, when 2 1/2 pounds was confiscated.

Authorities said Ibrahim Dende Borokinni, 32, of 1842 Longford Dr., was arrested about 2:30 p.m. Saturday, minutes after he arrived from London on British Airways flight 277.

"It was a cold hit," said U.S. Customs spokesman Jim Mahan, meaning that airport authorities had not suspected any passenger might be attempting to bring in narcotics. Customs agents began a search of the luggage because they "thought the passenger might be carrying food or plants" that cannot be imported, Mahan said. Instead, agents found what they termed an unusually heavy cigarette carton.

"They slit open one of the packs and found cellophane packages of heroin," Mahan said. "There were 10 cigarette packs and they were all filled with heroin."

Mahan said a thin blade apparently had been used to cut open one end of each pack. The cigarettes were removed, replaced with the small packets of heroin and the packs were resealed, he said. Investigators have not determined whether the smuggling attempt was the action of one person or part of the operations of a drug ring, Mahan said.

Borokinni, a Nigerian native, was charged with illegal importation of heroin and smuggling heroin, Mahan said. He was taken into custody by agents of the Drug Enforcement Administration and held overnight at Fairfax County Jail. He was arraigned before a federal magistrate in Alexandria yesterday and was being held at an undetermined location last night, officials said.

Investigators said they knew little about Borokinni's background, except that he was issued a U.S. work permit Sept. 20, 1982, and was a legal alien.

Mahan said a similar cigarette-pack technique was used by a major ring uncovered by federal authorities in 1978. Members of that group were charged with smuggling $30 million worth of high-grade heroin into the Washington area, concealing it in Marlboro cigarette packs.