FIVE or six years ago apartments went vacant in Cambridge. The "perennial" housing shortage is that recent. In the past six years, the median rent in Cambridge has doubled. And although the demand for additional housing is intense, hardly any appears.

A housing shortage has developed for various reasons, one of which is the attraction of new industries and business to the area. It may have taken the lead from NASA, which began to move into Cambridge in August of 1962. The '60's saw an increase in the number of new Cambridge-located research and development enterprises, new industries such as National Information Services, and greatly increased employee needs at Harvard.

Over a third of the total Harvard University student population-4020 persons-is now living off-campus. Landlords have recently developed a willingness to exclude family units by holding rents at levels which groups of students can afford to pay. While the national average for units of "unrelated individuals" living together is 18 per cent, in Cambridge 33.3 per cent of the housing is occupied by such groups.

Not counting the thousands of regular Harvard employees, there are close to 9000 students and Corporation appointees (administrators, professors, teaching fellows) occupying Cambridge housing. That alone is nine per cent of the total city population.

Another addition to Cambridge's housing market in recent years is Puerto Rican immigrants and people migrating from small towns in New Hampshire and Maine. With job cutbacks, many new arrivals are forced to turn to welfare programs.

Low to moderate income people suffer most from any bad economic situation. While 16 per cent of the Cambridge population is above the $15,000 income level, another 15 per cent falls below the poverty level. With 85 per cent of Cambridge rents higher than $100 a month, it is almost impossible for a family of moderate means to live in Cambridge.

Elderly people, most of whom have fixed incomes of less than $4000, are hardest hit by rising rent and by dislocation. The greater number of over-65's have roots here, and many have been forced out of their neighborhoods. Those who remain in their communities pay an average of 35 per cent (a comfortable amount is 20-25 per cent) of their income in rent alone.

WHAT is being done about the housing shortage in Cambridge?

There is too much talk, too many committees and proposals. Large-scale planning for the city doesn't exist. Responsibility for an overall housing polices plan lies with the Planning and Development Board, an arm of City Hall, which produced its last master plan for Cambridge in 1958. A new proposal is due sometime this year; and current judgments on zoning changes are done on an ad hoc basis. In order to maneuver, City officials and committees fail into compromise agreement which rarely result in action. Michael Rosenberg of the Planning Board terms making a master plan "an attempt at a rational decision process in the midst of an irrational political system."

Although there have been endless proposals launched, new housing has not kept up with demand in Cambridge. And with property values rising every day, there isn't much money to be made in low-to-moderate income housing, the level most sorely needed. Only the wealthiest of resources can acquire property and permission to build.

The largest (and richest) developer in Cambridge is Max Wasserman of Wasserman Development Corporation, who recently acquired the immense $51/2 million Bertha Cohen estate. He has numerous holdings in Boston and in Harvard and Putnam Squares.

Wasserman built the twin high-rise (22-story) buildings in Fresh Pond which house 500 moderate-to-low-income elderly and families. There is a waiting list for apartments in these eye-scrapers, where rent is proportionate to income and the elderly receive government subsidies. Having bought the land very cheap years ago. Wasserman profits well from the two Rindge buildings.

Although the new units do help to ease the tight housing market, less than half the residents are formerly from Cambridge, so the City's population is increased.

The Rindge buildings have problems inherent in that kind of sky-high living condition. Family units tend to become isolated from each other, and children don't come into contact with peers in the neighborhood area. They become restless, lacking direct access to the outdoors or companions. Wasserman neglected to install any sort of recreational facility which might alleviate some of the tensions of life in a non-neighborhood. The crime rate in the buildings has been very high. Another problem with Rindge is the inaccessibility of schools, which are over a mile away.

"I fear the sociological implications of such building," one housing expert said. "Those buildings are not for human beings."