A condominium apartment owner is more likely to be single than married, to comprise a one-person household, to live in a high-rise building where he or she formerly rented, to have an income over $30,000 -- and to be eminently satisfied.

So concludes a recent study by the urban housing research project of Northwestern University's Center for Urban Affairs. Interviews with 599 condominium-owners were conducted by a professional research group in Chicago, Houston, San Antonio, Denver and Washington, D.C., using questions devised by the Northwestern University center.

Louis H. Masotti, director of the project, said that the five cities were selected so that condominium life could be analyzed in various geographical regions and urban areas where "extensive condominium development has occurred in recent years."

Masotti refused to give names of any of the condo buildings in which owners were intereviewed due to "a prior agreement to protect the privacy of respondents." He did say that the average 45-minute telephone interviews were conducted with fewer than a hundred Washington area owners "in five or six buildings" in the District, Maryland and Virginia.

Masotti also said that more interviews were conducted among Chicago condo owners than among owners in any of the other four cities.

A summary of major findings from the Northwestern condo survey showed that condo owners tend to be older than most rental tenants but younger than homeowners in general. The median age of interviewed condo owners is 43.

Only 34.4 percent of the condo owners surveyed are married and live with their spouses. The remainder are single, separated, divorced or widowed.

Nearly 86 percent of those surveyed are "very satisfied" or "completely satisfied" with condo living.

One-third of the surveyed owners are married persons who have grown children living elesewhere.

The size of the condo household is smaller than that of renters and other homeowners. More than half of the con do owners live in one-person households and only 6.4 percent live in households with three or more persons.

Only 5 percent of the surveyed owners represent various ehtnic minority groups.

The average condo onwer is a college graduate, in contrast to renters and homeowners, most of whom have completed only high school.

Nearly 80 percent of condo owners are employed in white-collar positions.

Condominiums generally are purchased by persons who rented their previous homes and most of those surveyed lived in the building in which they bought a condo unit.

Condo purchasers, especially those under 45, made their choice primarily for financial reasons and most of them paid $50,000 to $70,000 for their units. f(Median purchase price was $56,650.) The purchase prices were higher in ratio to the age and income of the purchasers.

Sixty-three percent of the condo owners said they would buy another condo if they moved in the near future.

Only 43 condo owners reported personal involvement in condo-related disputes that included matters of property, finances, services, governance, life-style and personal well-being. More than two-thirds of the interviewed owners expressed satisfaction with their condo boards and associations.

In reporting why they chose to buy in a particular building, 28 percent said convenient location was the most important factor.

Copies of "Condominium Ownership: A Preliminary Analysis of a National Survey" are available from the Center for Urban Affairs, Northwestern University, 2040 Sheridan Rd., Evanston, Ill. 60201; attention - Audrey Chambers. The telephone number is (312) 492-3395.

In this area, where the conversion of rental apartment buildings and the contruction of new condo high-rise buildings have increased in the past 10 years, it is estimated that the current housing stock contains nearly 70,000 condominium units.