HARVARD HAS been in Cambridge as long as Cambridge has existed, and the University has made plans to stay around for at least another millenium. So it is difficult to imagine Cambridge without its universities, despite occasional pleas by local residents for the professors to pack up their bags and relocate on Route 128.

But there is no question that without the presence of Harvard and MIT Cambridge would have a totally different flavor. Almost every asset and problem of the city is derived in some way from these two schools.

The average Cantabrigian probably feels Harvard's presence most directly when paying his rent--over 80 per cent of the city's residents are tenants. Rent levels in the Boston area are the highest in the country, and Cambridge rents are the highest in Boston. The tremendous demand for housing in the area, caused by the influx of young people attracted to a university community, has made Cambridge a haven for real estate speculators.

Rents in the city have risen over 70 per cent in the last decade, despite the existence of rent control since 1970. Tenants can expect to pay about one-third less for equivalent housing in nearby cities which are similar in character to Cambridge (such as Somerville) except for the absence of a large university.

Both Harvard and MIT have begun crash building programs, both to house more of their own students and faculty, and to increase the supply of low income housing in the city. MIT recently completed three housing complexes for the elderly, while Harvard has several developments either under construction or in the planning stages.

The reaction to university construction has been decidedly cool, however, among both Harvard administrators and city residents. Jeffrey Leib of the Cambridge Tenants Organizing Committee said last week, "No one is really happy with all the high-rise university housing. As long as Harvard and MIT remain in the city, no amount of construction is going to meet the housing demand.

"High rises just make the city more overcrowded, and Cambridge is already one of the most densely populated cities in the country," he said. A little over 100,000 people live in the city's six and one quarter square miles.

Francis H. Duehay '55, a city councilor and dean of admissions at the Graduate School of Education, agreed last week that Cambridge does not need new housing units. "What we need to do right now is to work on rehabilitating the housing stock, which is pretty old and run-down," he said. Duehay added that cutbacks in federal housing funds have limited both rehabilitation and low-cost housing construction possibilities within the city.

ANOTHER SORE point between the city and the universities is their tax-free status. But Harvard and MIT voluntarily pay several hundred thousand dollars annually to Cambridge in lieu of taxes, and university-owned commercial property--such as the ground level of Holyoke Center--is fully taxable.

But these payments are a very small fraction of what the universities' tax bills would be if all their property were fully taxed--as many local politicians have demanded in recent years. It is doubtful that Harvard and MIT fully pay for all the services they receive from the city--especially in such areas as fire protection.

Yet, Cambridge tax revenues would probably decrease if Harvard and MIT were to leave the city. The two universities own only about 10 per cent of the city between themselves; if they left Cambridge, the tax revenue raised from their land could never equal the resultant drop in property values. Although the Cambridge tax rate is rising rapidly, it is still lower than most neighboring industrial cities, as a result of Harvard and MIT's presence.

In addition to money, Harvard provides a number of services to Cambridge residents. The Harvard Community Health Plan, a pre-paid group medical plan, has 36,000 members in greater Boston. Although now a self-sustaining, independent organization, it was conceived in the sixties by the Medical School. Harvard lent it several million dollars to get started, and all its doctors are affiliated with the Medical School.

Jerry R. Cole, director of membership of the plan, explained that since members pay for medical care in advance, they have an incentive to seek out the complete health care that they otherwise could not afford to receive. "Since we're not federally subsidized, we have basically a middle-class membership with only 4000 members from Cambridge," Cole said. "But we do provide complete care for over 250 Medicaid recipients from Cambridge, and are reimbursed for that care by the state."

Harvard has been less generous in its support of the Cambridge public schools. Most professors now either send their children to private schools or live in the suburbs, and thus they have done little to improve conditions in the city's less-than-adequate school system.

The Graduate School of Education worked with the school system in setting up in 1969 an experimental public high school to be run jointly by the Ed School and the city. But federal funds for the program ran out last year, and Harvard had to withdraw its support.