Mayor Marion Barry has rejected an appeal by tenant activists who had asked for his immediate support in seeking changes in the District's rent control law to protect tenants from what they say are unfair rent increases.

In a letter to the Tenant Organization Political Action Committee, the mayor said he wanted to await a study of the District's rent control law that is due in October. The $400,000 study was required when the D.C. Council extended the city's rent control law in 1985.

"We are not satisfied with the response we have received from the mayor," said Idus P. Holmes, president of the committee, at a news conference attended by tenant leaders, who said they would step up efforts to get council support for tenant legislation during this election year.

Rent control has been a volatile issue since it was first passed by the council in the 1970s. A coalition of council members in 1985 weakened the law but that action was overtuned in a referendum later that year. The committee was among several groups supporting the referendum.

One of the current goals of the committee, the organizers said, is to get council approval of a bill that would change how landlords are compensated for capital improvements of their apartments.

Under current law, landlords are allowed to continue to charge tenants higher rents for capital improvements, such as new stoves, even after the costs of such improvements are recovered. A bill introduced by council member Jim Nathanson (D-Ward 3), cosponsored by six other council members, would require that such rent increases be rolled back after the costs of improvements are collected.

The bill is pending in a council committee headed by John Ray (D-At Large), who has not yet scheduled hearings on it. Ray, a member of the coalition that previously weakened the law, said yesterday he was not blocking the bill's progress as some tenants have charged.

"When three members {out of the five on his committee} sign a letter and say, 'I want you to move the bill,' I'll move it," Ray said. Ray said he has told members of his committee the same thing but has received no response.

Nathanson and council members John A. Wilson (D-Ward 2) and Frank Smith (D-Ward 1) are members of Ray's committee. Wilson and Smith are cosponsors of Nathanson's legislation. The fifth member of the committee, Charlene Drew Jarvis (D-Ward 4), generally has been opposed to tougher provisions in the rent control law.

Ray said he also prefers awaiting results of the rent control study, which is being conducted by the Urban Institute.

Other changes sought by the tenant activists include new legislation to strengthen constraints on converting rental units to condominiums and limitations on how much rents can be increased when an apartment becomes vacant.

Nathanson also said yesterday that he was considering whether the District needs commercial rent control to keep smaller businesses from being "squeezed out to the malls and suburbs."

Nathanson said he already had begun receiving strong protests from some members of the city's business community for even mentioning the idea, including expressions of concern from Delano Lewis, a utility executive and president of the Greater Washington Board of Trade. "It's something I'm thinking about doing," Nathanson said. "I'm nowhere near articulating it so that it can be drafted into legislation at this point."