The race for the Democratic mayoral nomination in the District accelerated yesterday as John Ray won the endorsement of a longtime supporter of Mayor Marion Barry's, while rival David A. Clarke attacked Ray's stand on tenant rights and campaign contributions from developers.

Clarke, chairman of the D.C. Council, rallied with about 40 supporters in front of the District Building, where he attacked council colleague Ray (At Large) for votes that Clarke contended helped apartment owners at the expense of city tenants.

Ray, citing his support for rent subsidies for the poor, lifetime tenancy for senior citizens and other housing programs, said he has "done more for tenants than any other member of the council."

Meanwhile, Barry, in an effort to preserve some influence over the election of his successor, told his political lieutenants yesterday to hold on to their field organization and wait several weeks before transferring their support to another candidate.

"My advice at this point is to hold on until after July 5th," Barry said, referring to the deadline by which mayoral candidates must file voter signatures to win a spot on the primary election ballot this September.

"I don't think you ought to be petition-carriers for other people," added Barry, who earlier this month announced he would not seek a fourth term.

In a sign that the mayor's once-vaunted political machine is breaking up, a longtime Barry supporter, the Rev. A.C. Durant, pastor of Tenth Street Baptist Church, endorsed Ray yesterday as a new "Joshua to lead us forward."

"There is a new sun on the horizon, there is a new day coming," Durant told a crowd of 400 people who gathered at his church in the District's Shaw neighborhood to hear Ray issue an appeal for racial unity in the city.

"I do not want Washington, D.C., to suffer the racial and ethnic division that I read about and see in New York City," Ray said. "I am determined, and I ask you to join with me today, to stop such harm from taking root."

Ray outlined a strategy to reduce racial divisiveness, including promoting cultural exchange programs between neighborhoods and promising to speak "loudly and clearly against bigotry and hatred."

Clarke sought to escalate his attack on Ray for Ray's role in a 1985 council debate about the gradual phase-out of rent control.

The council narrowly approved a rent decontrol bill that year, but it was overturned within months by a citywide referendum. Ray and council member Charlene Drew Jarvis (D-Ward 4), who is also running for mayor, campaigned against the referendum.

Clarke also criticized Ray for taking many large campaign contributions from developers and landlords. Ray is the leading fund-raiser among the mayoral candidates; of the nearly $550,000 Ray had raised through February, about one-third came from real estate interests.

Ray dismissed Clarke's attack, saying that while the council chairman "has 40 people putting out misinformation, I'm speaking to 600 trying to bring our city together."

Ray also asked whether Clarke and D.C. Del. Walter E. Fauntroy, a mayoral candidate who has criticized developer contributions, would return money given to them by those and other special interests. Clarke and Fauntroy have received developer contributions, but considerably fewer than Ray.

Barry sought yesterday to play down recent speculation that he was poised to deliver his still-considerable political organization to Jarvis.

After noting reports that he would soon embrace Jarvis's candidacy, Barry told his supporters: "That's not true." Later, when asked by a reporter if he planned to endorse Jarvis, Barry replied: "No, no, no, no . . . . I've not committed to anybody at this point. Unequivocally -- I didn't commit to anybody."

However, sources said Jarvis, who has carefully avoided attacking Barry directly in the months since his January drug arrest, remains hopeful about receiving the mayor's blessing, perhaps as early as this week. "There are people within the mayor's organization who are on our team," Jarvis said yesterday, adding, "The timing of an announcement of support {by Barry} is critical."