A private study commissioned by the city has recommended abilition of the District's rent control law, citing deterioration of building maintenance and stagnation of apartment construction as major results of the law.

The study, which has not been made officially public, comes at a time when City Councilwoman Nadine Winter, head of the Council's housing committee and onetime champion of rent control, has proposed new legislation providing for a gradual phaseout of the present law beginning in mid-1980.

Lorenzo Jacobs, director of the city's housing department, which commissioned the $66,000 study, joined the growing list of officials who say they are disillusioned with rent control. He told Winter's committee in public hearings Tuesday he not only supports elimination of rent control out recommends that decontrol begin next year with completion by July 1, 1980.

The purpose of the private study conducted by Development Economics Group, a consulting organization at 1010 Vermont Ave. NW, was to assets the impact of rent control in the city. Its major findings were:

Rents in the city have increased less than in the surrounding suburbs since rent control went into effect in the city in 1973. Suburban Maryland jurisdiction have had rent control but are now either phasing it out or have eliminated it entirely. Northern Virginia had had no mandatory rent control.

Garden apartment owners - as distinct from so-called elevator building owners - have lost money with rent control in the city and "have seen either a reduction in net income or have deferred maintenance." Operational costs for garden apartment projects increased an average of 9.2 per cent from 1974 to 1975, the period included in the study, while average operating costs for elevator buildings increased only 1.8 per cent.

No rental apartment construction has taken place in the city since 1973.

The study recommended that the city begin dismantling its rent control apparatus because of its "many deleterious effects to the housing stock."

Winter said Wednesday she had proposed legislation to phase out the program because, "there has not been any new construction and we have to deal with that." She added, "All the counties are moving away from rent control."

Prince George's County dropped its rent control program a year ago and Montgomery County is phasing out rent control. All vacant units were decontrolled last July, and all rent controls are scheduled to end on Dec. 31.

According to a survey conducted by the Montgomery Landlord Tenant Office, during the first six months of decontrol of vacant units, rent for these units had increased only 9 per cent above what they had been under rent control.

The county's rent control law had allowed landlords an automatic 4.5 per cent increase annually.

David Shikles of Development Economics Group told the Winter committee yesterday that the reason owners of elevator buildings had gained an 8 per cent increase in their net income from their property was "not because rents have increased but (because) the operating expenses barely moved from one year to the next."

The study esitmated that 120,000 of the city's 180,000 apartment units were garden apartments while the remaining 60,000 units were located in elevator buildings.

Both Winter and Jacobs have voiced concern that low-income tenants may be adversely affected if rent control ends. Both said yesterday they support a rent subsidy program financed by the city. Jacobs added that his support was contingent on the availability of money to finance such a program.

According to the consultants' study, 23 per cent of the city's tenants paid more than 35 per cent of their income for their rent, and most of these were poor families.