Only six months after they helped defeat a referendum initiative for rent controls, San Francisco's middle-class apartment dwellers are rising in revolt and calling for establishment of rent controls.

Spurred by one landlord's rent increases of between 20 percent and 62 percent in 1,100 apartments last month, tenants have begun organizing, have been conferring with lawyers over the ground rules for rent strikes, and have pressured the city's board of supervisors into declaring a 60-day moratorium on rent increases.

The uproar has split the real estate community, galvanized the city government into frenzied activity, and solidified a coalition of low-income, moderate-income and downright affluent tenants into what most observers see as an unbeatable drive for rent control.

In addition to the moratorium, the supervisors appointed a special five person committee to consider alternatives for the board's consideration at the end of the 60-day period.

Meanwhile, Mayor Dianne Feinstein has come forward with her own proposal for a rent arbitration board to settle disputes between landlords and tenants.

San Francisco's sudden move into rent control exemplifies the pressures many urban renters are experiencing in hot markets and also illustrates the tight confines of the "social contract" between renters and owners which can be overstepped only at great risk.

The city's middle-class tenants helped defeat an initiative last November by a slim, but decisive margin of 53 percent to 47 percent. Real estate interests at the time concluded that the vote showed residents were prepared to accept the high costs of renting in attractive urban settings but expected landlords to observe certain "unwritten rules" about rent increases and provision of services, particularly in the wake of Proposition 13 tax windfalls.

So long as the quality of life in rented properties was maintained at reasonable levels and increases were kept to a moderate pace, the city's tenants seemed to be saying they preferred an unregulated rental market.

But landlord Angelo Sangiacomo changed all that when he announced hefty increases ranging up to 62 percent in 1,100 units all over the city in mid-April. Most of his tenants live in well-appointed buildings with plenty of amenitites. They also are well-educated, articulate and not intimidated by the hurly-burly of city politics. When the increases came down, reaction was instantaneous. Meetings were announced through signs pasted in downtown apartment building windows and scores of residents turned out to see what could be done.

The tenants are the first to acknowledge they're not suffering financially. One is a vice president of Crocker National Bank. Another is the senior vice president of a major engineering firm. But they all argue that they already are paying premium rents to live downtown and that Sangiacomo has reaped nearly a quarter-million dollars in tax savings this year alone because of Proposition 13 property tax reductions. Services in the buildings were not improved and rent schedules are inconsistent even within buildings, tenants say. They charge that Sangiacomo merely is trying to squeeze them for all he can get, whether the increases are justified or not.

Although Sangiacomo argues that his buildings are still the best value in town, and has offered his tenants sizable rebates if they can find something similar or better for less, the mayor and some major local estate figures have tried to talk the maverick builder into backing off his position. But the landlord has held firm, agreeing only to hold off collecting the increases until after the board of supervisors has reached a decision. CAPTION: Picture, DIANNE FEINSTEIN . . . proposes arbitration board