No matter how it is viewed, the Washington area apartment rental market enjoys a high occupancy ratio, with over-all vacancies around 3 per cent.

Rents have been moving up, even in an aura of real or implied constraints. New construction has been sluggish for several years but the pace is now accelerating, specifically with the availability of below-market interest rates with federal subsidies.

However, there is some apprehension that the expected formations of new housesholds and the usual toll of obsolescence will require approximately 23,000 new units a year to maintain a stock of more than 400,000 rental dwellings. Approximately 40 per cent of the area's households rent their homes.

Also to be considered is the growing number of conversions of large rental complexes, such as Fairlington and Parkfairfax in Northern Virginia, to condominium ownership.

In terms of new construction, starts of multi-family dwellings here fell to 2,324 in 1975 and rose slightly to 3,263 in 1976. This year, some 5,200 units are expected to be started to be started. In the mid-1960s, apartment starts exceeded 30,000 units annually in this area. Based on a 50-year life expectancy for most rental units, some 8,200 units need to be built each year to maintain the housing stock we now have.

Sidney Glassman, president of the Apartment and Office Building Association of Metropolitan Washington, observes that most new construction now is confined to federally subsidized or insured programs for rental housing. He said that new, privately built rental apartments will most likely be located in Northern Virginia.

W. Bruce Steele, associate director of housing programs for the Metropolitan Washington Council of Governments, estimates that nearly 70 per cent of all new apartments built this year will have federal assistance. He estimates that the area's vacancy rate is 3 per cent, with Arlington County having the lowest at about 1.2 per cent and Prince George's County the highest at 4 per cent or more.

Since 1972, an effort has been made through the Council of Governments to use a "fair share" procedure among area jurisdictions in building rental housing for low-and moderate-income families. COG's Patricia Heinaman said that the objective is to meet housing needs and expand opportunities. She estimated that 2,700 new units of "fair share," federally assisted housing are under way here. Some 9,000 such units have been built in the region since 1972, she said.

Among private lenders, mortgage banker John D. Reilly says his firm has been arranging loans for a number of subsidized apartment projects, particularly those for the elderly.

Beilly and his business associate Gaye Beasley say that apartment construction has not kept pace with demand in this area and that rent increases have barely kept pace with the upsurge in operating expenses. Reilly said that the over-all range for garden apartmeent rents now is 20 to 30 cents a square foot per month for existinng facilities and usually 30 to 40 cents per square foot in a high-rise.

He thinsks new apartments will be smaller and cost more, and notes that two new privately financed apartment buildings in the District drew tenants willing to pay more than 50 cents per square foot - in other words, rents higher than $500 for a typical apartment.

"There's a generally a tight rental market for the for predictable future and rents likely to move up 30 per cent in the next two or three years," added Reilly. "Heating and cooling costs are one reason - more future rental dwellings will have separate heating-cooling utility bills.

Meanwhile, he said, "more people will opt to buy to counteract inflation and to take advantage of tax deductions," at the same time sacrificing mobility and the carefree aspects of renting.

One Silver Spring builder, Thomas P. Harkin Construction Co., has four subsized housing projects under way. Two buildings slated for the elderly - the Bauer Drive rental dwellings on Route 28 east of Rockville and the seven-story Leafy House in Wheaton - are sponsored in part by the Montgomery County Housing Opportunities Commission.

Additionally, the Harkins firm is building units (under the Section 8 rent subsidy program) in an urban renewal area in the northern part of Old Town Alexandria known as "the Dip." The National Housing Partnership is a co-sponsor. In another moderate-income project, in Bethesda, Harkins is doing the 158-unit Waverly House high-rise on East-West Highway for Danac Corp. and the Montgomery housing commission.

The Silver Spring-based Construction General, Inc., headed by Bernard Lubcher, is using 7.5 per cent, Brooke-Cranston funds for a 10-story, 268-unit rental building near Connecticut Avenue and Van Ness Street NW, on land formerly owned by the now-defunct Dunbarton College.

Lubscher said the firm also is also constructing 406 rental units on an urban renewal site at Columbia Road and 14 Street NW under the federal Section 236 housing program. The project is co-sponsored by a neighborhood organization, Change Economic Development Corp., and All Souls Unitarian Church.

The firm is also submitting feasibility studies to the Department of Housing and Urban Development for Section 8, rental subsidy housing projects on Democracy Boulevard in Montgomery County and at Tysons Corner in Fairfax County.

A.D.C.-based developer, the Holladay Corp., has completed and nearly fully rented the conventionally financed, 860-unit Connecticut Heights project on upper Connecticut Avenue, a complex of two high-rise and four-low-rise buildings. Rents average 52 cents a square foot where utilities are included. Rents start at $230 a month for an efficiency and stop at $575 for a two-bedroom unit.

Another large Holladay project is north of Laurel at Whiskey Bottom in Howard County, where there's a waiting list for garden apartmetns ranging from $240 to $340 a month. An earlier section was done with FHA program financing but recent sections of the 1,100-unit rental complex are conventionally financed.

It appears then, that future apartment construction here is likely to be federally assisted, with major emphasis on housing for the elderly, such as the high-rise now under construction at the Fort Lincoln new town.

Where feasible, some developers may initiate privately financed rental developments, especially if financing costs ease.

There is talk that one local developer may undertake a luxury apartment project on part of the Foxhall-Glover tract south of American University. Such a project would command rents of 70 cents a square foot, or about $1,400 a month for a big, two-bedroom apartment with 2,000 square feet of space. Luxury condominiums that size are selling now for more than $100,000.