All of them say they are for it, right up there with mom and apple pie.

Yet as the primary campaign turns for home, the five Democratic candidates for D.C. mayor are sniping more and more over an issue that comes wrapped in a phrase of bureaucratese: rent control.

What they dispute is the depth of each other's commitment to the system the District uses to regulate how much landlords can increase rents in the city's 120,000 rent-controlled apartments.

It is a potent issue.

"Two-thirds of the people in the city are renters, and we're talking about their pocketbooks," tenant activist Gottlieb Simon said last week, adding that many renters will decide whom to support for mayor solely on a candidate's enthusiasm, or lack of it, for controls.

At the heart of the squabble are the three candidates who serve on the D.C. Council -- Chairman David A. Clarke, at-large member John Ray and Ward 4 member Charlene Drew Jarvis -- and what they did during a clash over renewal of the rent restrictions five years ago.

At that time, the controls had been in place for about 10 years. The basic provision was that rent increases were pegged to the consumer price index, but that no apartment's rent could rise more than 10 percent a year. Clarke proposed a bill to keep the system as it was.

But Ray, arguing that housing construction was being hurt because landlords could not get a fair return on their investment, suggested that controls be lifted on apartments as they became vacant, if certain conditions were met. He also proposed a fund to help tenants who had trouble paying their rent.

Tenant groups objected bitterly, saying the lifting of controls on vacant apartments would lead to a rise in rents and might cause landlords to evict tenants to increase rents.

Jarvis proposed a compromise, which became law, that generally made it easier for landlords to raise rents but provided for the tenant-assistance fund. In a referendum in the fall of 1985, however, some of the new provisions were repealed.

To some tenant activists, the lesson of those episodes is clear: Clarke was a hero. He wanted to continue a system they felt had kept rents down, and they have now endorsed him for mayor.

But Ray, they say, showed he was the landlords' man, and they contend that the 1985 bill has led to tremendous rent increases in some buildings. Jarvis's role of championing the compromise was only slightly less odious, they say. What the activists say they find especially irritating is that Ray and Jarvis have portrayed themselves as friends of renters.

"It would seem to me they ought to be called hypocrites," said David Conn, chairman of the legal and legislative committee of the Tenant Organization Political Action Committee, or TOPAC, a group representing 27 tenant organizations.

Simon, who labeled as grotesque a Ray brochure that says he has backed rent control, said Ray has "continued to be a major roadblock" to better rent control. But he said Jarvis "has moved closer to tenant positions and has clearly sought to distance herself from John Ray, with whom she previously had been a clone on landlord issues."

In a debate Friday, Ray said he would support extension of the rent control law when it expires in 1995.

Not surprisingly, Clarke has sought to capitalize on the 1985 debate, urging tenants to remember Ray's and Jarvis's positions. Del. Walter E. Fauntroy, another mayoral candidate, has joined the attack on Ray.

Jarvis said Clarke was attempting "to galvanize mass hysteria" and was "grabbing for an issue." But she then turned the issue on Ray.

"It's a viable issue," Jarvis said, because "Ray is so heavily supported by real estate interests whose driving passion is to get rid of rent control." She characterized her role in 1985 as bridging the gap between Clarke and Ray, but said that she is now convinced tenants are being hurt by some aspects of the law.

Ray said his bill was "not trying to end rent control" but "trying to get an incentive to get the boarded-up buildings of Southeast and Northeast on the market."

"I don't think the election's going to be settled on this issue," he said.