The two suspects in the Boston Marathon bombings led police on a wild and deadly chase through the suburbs here early Friday morning that ended in the death of one of the suspects as well as a campus police officer; the other suspect remained at large while hundreds of police officers conduct a manhunt through Watertown, about five miles west of downtown Boston

The Boston region was in the grip of a security emergency as hundreds of police officers conducted a manhunt through the normally tranquil Boston suburbs.

Gov. Deval Patrick has suspended service on all public transit services in the M.B.T.A. system in Boston, including the “T” subway, buses and commuter trains. The authorities asked all residents of the towns of Watertown, Newton, Waltham and Cambridge to stay home and stay indoors. Watertown was locked down early Friday morning, with no one allowed to leave their homes and no businesses allowed to open.

Several area colleges announced the cancellation of classes on Friday, including the Massachusetts Institute of Technology, Harvard, Boston University, Boston College, Emerson College, Northeastern University and Suffolk University.

“This situation is grave, we are here to protect public safety,” said Col. Tim Alben of the Massachusetts State Police.

“We believe these are the same individuals that were responsible for the bombing on Monday at the Boston Marathon,” Colonel Alben said. “We believe that they’re responsible for the death of an M.I.T. police officer and the shooting of an M.B.T.A. officer.”

In the course of the chase, the suspects shot and killed a campus police officer at M.I.T. and severely wounded a transit police officer, police said. The authorities were investigating whether the suspect who was killed had an improvised explosive device strapped to his body, two law enforcement officials said.

Edward Davis, the Boston police commissioner, told reporters early Friday morning that the two men involved in the chase were the suspects identified Thursday by the F.B.I. as responsible for setting the explosives at Monday’s marathon that killed three people and injured more than 170 others.

He also said that one of the suspects, wearing the black hat in the F.B.I. photos, was dead and that the other suspect, in the white hat, was still on the loose.

Early Friday, a virtual army of heavily armed law enforcement officers was still going through houses in Watertown one by one in a search for the second suspect. Police had blocked off a 20-block residential area and urged residents emphatically to stay inside their homes and not answer their doors.

“We are concerned about securing that area and making sure that this individual is taken into custody,” Mr. Davis said. “We believe this to be a terrorist. We believe this to be a man who’s come here to kill people, and we need to get him in custody.”

With gunfire ricocheting around the tranquil neighborhood, residents were later told to go into their basements and stay away from windows.

The pursuit began after 10 p.m. Thursday when two men robbed a 7/11 near Central Square in Cambridge. A security camera caught a man identified as one of the suspects, wearing a gray hoodie.

About 10:30 p.m., police received reports that a campus security officer at M.I.T. was shot while he sat in his police cruiser. He was found with multiple gunshot wounds, according to a statement issued by the Middlesex acting district attorney, Michael Pelgro; the Cambridge police commissioner, Robert Haas; and the M.I.T. police chief, John DiFava. The officer was taken to Massachusetts General Hospital, where he was pronounced dead.

A short time later, police received reports of an armed carjacking of a Mercedes S.U.V. by two men in the area of Third Street in Cambridge, the statement said. “The victim was carjacked at gunpoint by two males and was kept in the car with the suspects for approximately a half hour,” the statement said. He was later released, uninjured, at a gas station on Memorial Drive in Cambridge.  (Page 2 - separate post)