It is 4:30 in the morning on a bitterly cold fall day in Boston and there has just been an accident in front of the Harvard-affiliated Deaconness Hospital. A taxicab has crashed into a passenger car. The Harvard Police patrol car assigned to the Medical Area arrives at the scene and takes down the cab operator's license. While one policeman remains at the scene of the accident, the other telephones in the license number to the department's Garden Street headquarters. Within minutes, a national check on the driver's record has been performed. Police arrest Bruce Nance, 42, of Boston, on rape charges; Nance has been wanted for five years by Boston Police.

This fall Harvard took a giant step toward bringing its police force into this age of modern communications by purchasing a special computer for the Police department. After four months of starting practice, the system is fully operational and police say it is proving even more useful than they had hoped.

Among other functions the $30,000 Durango computer can:

*Analyze crime patterns in a particular area, or even building, allowing police to concentrate their force on trouble spots;

*Track the history of stolen goods. Police can pinpoint, for example, the number of bicycles of a particular make stolen from the Science Center each week since the system was installed.

*Shorten from about seven minutes to 20 seconds the time required for an identity check of a suspect. The computer identifies, dates and describes every contact the Harvard Police have recorded and can provide a printout upon request.

*Produce customized summaries of crimes for House masters, building superintendents, deans, news organizations and a variety of other groups interested in campus crime.

The nerve center of the Police Department's glossy new headquarters is the dispatch room that sits, protected by a huge pane of plate glass, in the center of the building's suite of offices.

Communications clerks sit here 24 hours a day, directing the flow of police around the University. The equipment in the room has changed little since the room was built in 1979-with one exception: a wheeled trundle, installed this summer, now brings a computer terminal within inches of the clerk's elbow.

The new computer replaces the cumbersome arrangement the department had used for several years, when data was entered at a mainframe computer at the Business School, printed out, and carried back to the police department.

"It was very difficult to work with," says Donald C. Nagle, the department's management information systems coordinator. Nagle has been a backer of computerization for years, he says, and is currently in charge of the Durango system.

"We were on a timesharing basis there [at the Business School]-our access to the system was no better than students here on course computers," he adds. And, Nagle says, the previous system was ill-suited: "It was difficult to use and expensive to make changes." Business School bills could run into hundreds of dollars for just minutes of the mainframe computers time, Nagle says. The new computer will pay for itself in three years, officials estimate.

The Durango system makes use of software designed especially for small police departments by the Illinois computer company CES Telecommunications. So far the Harvard force is the only one in the country to use this program. "This is new software specifically designed for our department," Nagle says.

CES is also working on a customization of the Harvard system for the police department in Northfield. Illinois, a town of 5000 with a police force roughly the size of Harvard's. Northfield also plans to purchase a Durango computer.

"It still has to be approved by the village Board of Trustees, but we're hoping to get it within a year," says George A. Wagner, deputy chief of Northfield Police, who has been in charge of computerizing the force. He cities the same reasons as Harvard officials for buying a computer: "We're currently using a computer in central Illinois for data analysis, and that takes months. We need our own machine for statistical data analysis."