Since its inception in 1970, rent control has held center stage in Cambridge politics.

Other issues come and go, but the city's rent control system remains as controversial today as the day it was enacted. And in every election, rent control is a battleground between candidates favoring the system's overhaul and those rallying for its preservation at any cost.

This election year, however, the debate has a different spin. With three of rent control's strongest backers retiring from the City Council, the future of the system could be in jeopardy.

More importantly, city residents will vote this year on Proposition 1-2-3, a binding ballot referendum that would fundamentally change the system by allowing some tenants in rent-controlled housing to purchase their apartments after living in them for at least two years.

Supporters of the measure say it will give thousands of city residents an opportunity to buy homes, which they otherwise could not afford. But 1-2-3 opponents contend that the proposition would cripple the rent control system and dangerously deplete the city's stock of affordable housing.

Heavily backed by Cambridge's real estate industry, the pro-1-2-3 lobby contends that its opponents are insensitive to the needs of low-income city residents.

"I think they're just upset because they haven't done anything to help [those with low incomes]," says Rosemary D. White of the pro-1-2-3 Cambridge Homeownership Association (CHOA).

But 1-2-3 opponents say the referendum is deceptive because it claims to promote affordable housing while actually gutting rent control, its main component.

They say that there are plenty of condominiums available to those tenants who wish to buy one. And they dismiss as "inflammatory" campaign hyperbole White's contention that homeownership is "illegal" in Cambridge.

"People can buy apartments," says Pamela A. Bender of the Committee to Defeat Proposition 1-2-3. "They just can't buy rent-controlled apartments."

And Bender and her cohorts say that approving Proposition 1-2-3 would not even help tenants purchase their apartments. Proponents of the referendum argue that the apartments would be sold perhaps as much as 50 percent below the market price because each apartment would have only one possible buyer. But a study sponsored this summer by those opposed to Proposition 1-2-3 concluded that significant discounts are unrealistic.

"That was an argument based on rhetoric and not too much else," says Kennedy School student and study author Patrick J. Dober of the discount theory. In fact, Dober found, the average discount 1-2-3 would give tenants is a mere 8 percent.

Dober based his study on the premise that the first part of 1-2-3 would place tenants in a position similar to that of tenants who lived in rent-controlled apartments before the city's Removal Permit Ordinance of 1979.

By examining the purchase price paid by pre-1979 tenants for their apartments and comparing it to the estimated market price, Dober came up with the 8 percent figure.

But Cambridge realtor Frederick R. Meyer--Proposition 1-2-3's author--argues that the 50 percent figure is an accurate one. He says Dober's study has a false premise, adding that the Kennedy School student calculated figures in an unorthodox way, resulting in misleading statistics.