A State Police helicopter crashed through the Harvard Yacht Club building yesterday morning, killing all four passengers, including two state police troopers and two American Telephone and Telegraph (AT&T) employees who were working on a state contract.

According to State Police officials, the helicopter took off at approximately 9:30 a.m. from the State Police's helipad on Nashua Street in Boston and was heading for Norwood Airport.

Less than one minute after takeoff, the aircraft plunged 400 feet and fell through the roof of the Yacht Club building, on 45 Memorial Drive, at about 9:33 a.m., said eyewitnesses on the scene yesterday.

Rescuers from MIT's emergency response team, who were training near the crash site, said they were not initially prepared to deal with the wreckage.

"We didn't have any of our equipment with us," said David M. Barber, MIT's utilities construction coordinator. "We just dealt with what was there. There was no time to get equipment; we just acted as best we could on the spot."

All four passengers aboard the eight year-old American-made helicopter were pronounced dead at the scene.

The two state troopers, James Mattaliano, 33, of Sandwich, and Paul A. Perry, 39, of Salem were 12- and 14- year veterans of the State Police, respectively.

Also killed in the crash were longtime AT&T technicians Arthur T. Howell, 47, of Everett and Michael McCarthy, 46, of Weymouth.

"We're in quite a bit of shock. It's been a very difficult year for the State Police," said State Traffic Reporter Grant Moulaison. "Obviously, our hearts go out to their families."

Police officials said yesterday that both troopers were licensed pilots, but it is unclear who was flying the helicopter at the time of the crash.

Mattaliano had been a pilot for one year and Perry had been flying for six years.

And although the crew had communicated with the Logan Airport Control Tower, a distress signal was not transmitted, said Col. Charles Henderson, Superintendent of the State Police, at a press conference yesterday.

Aviation experts speculated that the pilot was attempting to land in the Charles River.

"We are trained to go for the water or for the road," said Dean R. Bennett, chief pilot for the State Police. "If he could not land on the road because of traffic, he would obviously have tried to go in the water."

Bennett said that Memorial Drive was probably congested at the time of the crash, forcing the pilot to head for the river.