Just before noon Thursday Georgetown University freshman Rita Fallon walked up to the door of the New South Dormitory, pulled a plastic computer coded card from her pocket and inserted it in a slot.

In milliseconds, an electronic scanning device scrutinized the card and passed along certain information to a computer housed in the basement headquarters of the campus security force a short distance away. Instantaneously, the computer verified her status as a student and unlocked the door at New South:

At the same time, there flashed on a screen above the computer console, information that a student had just opened the north exterior door of New South. And, for the record, a printout a few feet away recorded the time the door had been opened and Fallon's computer code number so that, should they need to know, officials could learn the identity of the student who entered New South just before noon.

Such incidents are repeated thousands of times daily at Georgetown where on of the most elaborate and sophisticated campus security systems in the nation has been installed to cut down on campus crime. Symbolically, that system is reflection of a changing era when the kindly but often ineffectual campus cop of a generation ago has been replaced by a trained and disciplined security force using the best of modern technology to fight campus crime.

"Everbody is concerned about security and we must do everything we can. It's a burgeoning field," says Charles E. Lamb III, a retired New York City police lieutenant who is now Georgetown's director of public safety.

Reported theft losses have dropped about 25 per cent and trespassing incidents by about 50 per cent since the new system was installed 18 months ago, Lamb said.

Even so, theft losses in the dormitories still run at about $40,000 a year, and there are about 150 to 160 incldents of trespassing, most by juveniles, he said.

At a cost of about $85,000, Lamb has had installed an individually coded keyard system in which a computer controls access to all dormitory doors and only persons with the proper cards can unlock them.

"To my knowledge, it is the only college keycard type access system in the country," says James L. McGovern, the executive secretary of the International Association of College and University Security Directors.

"There are other institutions very much interested in this type of equipment," said McGovern. "There is an awareness on the part of campus administrators that they must provide quality security."

Over the last few years, as students at campuses throughout the Washington area have increasingly become the victims of theft, assault, robbery and even rape, security has been increased in a variety of ways.

At Catholic University, William Nork, a retired military police officer who once headed U.S. Military Plice in Saigon, has been hired to reshape campus police operations.

Nork has hired younger campus policemen, purchased high speed "pursuit vehicles" to chase criminals with and increased the number of hotlines on campus with immediate access to campus police.

At the Georgetown University Law Center on New Jersey Avenue NW, direct telephone lines to security officers have been installed in all the women's rest rooms.

State policemen patrol the campus of the University of Maryland at College Park, but many students still complain that security needs to be tightened. One woman who graduated last May by her dormitory bed and was afraid to take a shower or go to the bathroom late at night.

With the card access system at Georgetown, students are given cards that permit them to enter dormitories 24 hours a day. But cards for maintenance and housekeeping employees permit them access only during their assigned working hours and then only to the areas where they are assigned to work. If [WORD ILLEGIBLE] cards are used to other times and places, the computer is programmed to keep the doors locked.

Additionally if a student loses his card, he can be issused a new one and the computer can be programmed to reject the old card.

"We can take anybody out of the system at any time. We can put anybody in the system at any time," says safety director Lamb.

"It's good security," said freshman Mary Louise Burns of Birmingham, Mich. "I come in late at night and I know there won't be any strangers inside the door."

About the biggest problem with the system, says Lamb, is what's known as "piggybacking" - one student opens the door with his card and seven or eight others follow him in before the doors close.