MOSCOW--A family of musicians from Siberia who hijacked an Aeroflot jet hid their weapons inside their instruments, then opened fire and set off a bomb when an army assault team stormed the grounded plane, Soviet media said yesterday.

Five of the hijackers, who were led by two brothers and their mother, died in the assault and subsequent fire aboard the jetliner on Tuesday, as did three passengers and a stewardess, Tass said. Two of the sky pirates committed suicide and the matriarch, once honored as a Hero Mother of the Soviet Union, was shot dead by family members, the official news agency said.

Deputy Civil Aviation Minister Ivan Vasin told the government newspaper Izvestia that the hijacking was the most dramatic he could recall in his long career.

Eleven hijackers commandeered the Tupolev-154 jet as it was en route to Leningrad after a fueling stop in the Ural Mountains city of Kurgan, and they told the pilot to fly to London, Tass said. It identified them as the Ovechkins, a family musical group from Irkutsk, the southern Siberian city where the flight originated.

"Eyewitnesses pointed to three leaders among the criminal team--Vasily and Oleg Ovechkin and their mother Ninel Ovechkin, a plump, fashionably dressed woman of over 50," Tass said.

"They had brought the weapons and explosives aboard the plane in their musical instruments," Tass reported. It gave no details of the Ovechkins' background and did not say how they managed to elude airport security.

Pre-flight checks at airports in the Soviet Union are not uniform and range from screenings by metal detectors, friskings and a meticulous search of carry-on baggage to a perfunctory glance at passengers' tickets.

The airport at Irkutsk, 2600 miles southeast of Moscow, is a major hub for flights throughout Siberia, and is often jammed with people who sometimes wait for days to make connecting flights.

About 3 p.m. Moscow time, while the Tu-154 with 76 passengers was over the Vologda region east of Leningrad, the hijackers sent a note to the cockpit, Tass said.

Izvestia, in its report on the hijack, quoted the note as saying: "Fly to a capitalist country [London]. Don't fly any lower. Otherwise we'll explode a bomb."

The flight crew contacted the ground, and a plan was worked out to dupe the hijackers into thinking they were landing in Finland.

The assault team was waiting when the Tu-154 touched down at a field near Leningrad, Tass said.

The Sovietskaya Rossiya daily said the four-man flight crew, led by Pilot First Class Valentin Kupriyanov, kept their heads when confronted by the hijackers' demands.

"After landing, the crew entered into negotiations with the bandits, asking them to give up their criminal intentions and not to endanger passengers' lives," the newspaper said.

But the hijackers refused to listen, it said.

"With every passing minute, they became more aggressive, and started to behave like hooligans in the cabin. The armed bandits threatened to kill passengers."

"Under those conditions, the only decision that could be taken was to render the criminals harmless," Sovietskaya Rossiya said.

They set off a bomb in the airliner's tail section, setting the plane on fire, Tass said, "An air hostess and three passengers were killed as a result of this terrorism," it said.

"Five of the 11 criminals were killed," Tass said, without giving details.

Izvestia quoted witnesses as saying one hijacker died in the bomb blast, two others committed suicide, and Mrs. Ovechkin had been shot dead by some of her fellow hijackers.

Mrs. Ovechkin at one time had been honored as a Hero Mother of the Soviet Union, the newspaper said. The decoration is given Soviet women who have many children.

Hijacking in the Soviet Union can be punished by death.