The two leaders in the now-crystallizing Democratic primary for D.C. mayor traded blows Wednesday night in the last televised debate of the contest, but neither landed a knockout punch that would threaten to alter its trajectory.

Incumbent Vincent C. Gray and D.C. Council member Muriel Bowser, leaders of a newly published Washington Post poll, tussled over the former’s involvement in a federal investigation and the latter’s readiness to serve as mayor. But their statements only occasionally illuminated fresh contrasts or highlighted new contradictions.

The hour-long debate on ­WUSA-TV (Channel 9) was the last broadcast debate scheduled ahead of Tuesday’s primary, closing out months of candidate encounters in settings ranging from intimate church basements to rowdy auditoriums.

A final mayoral forum, sponsored by the Jewish Community Relations Forum, is set for Thursday evening at a synagogue in Chinatown.

Under questioning Wednesday from WUSA reporter Bruce Johnson, Gray repeated denials of wrongdoing during his 2010 campaign effort and said his challengers have a “vested interest” in promoting the allegations made against him. “They want my job,” he said.

Bowser (Ward 4) said she believes that Gray knew of hundreds of thousands of dollars in illegal, secret spending made on his behalf by city contractor Jeffrey E. Thompson.

“People know all of the allegations, they know that there may be an indictment, they know that the mayor deserves the presumption of innocence, and still they say they don’t trust this mayor,” she said. “They do not want to drag this scandal into the next four years.”

The debate — which also included council members Jack Evans (Ward 2) and Tommy Wells (Ward 6) — came as Gray struggles to build upon his loyal base amid the new corruption allegations; Bowser tries to gather anti-Gray sentiment behind her; Wells seeks to gain elusive traction with an ethics-focused message; and Evans, the council’s longest-serving member and a second-time mayoral candidate, again watches his aspirations slip away.

A Washington Post poll published Tuesday showed Gray and Bowser in a statistical tie, with the respective support of 27 percent and 30 percent of likely Democratic voters. Only Wells also showed support in the double digits, with 14 percent in a survey that carried a 6.5-point margin of error.

A lengthy exchange centered on the legacy of former mayor Adrian M. Fenty, who endorsed Bowser to replace him in the council seat she now holds. Gray and Evans sought to portray Fenty’s administration as marked by fiscal mismanagement, based on the depletion of city reserve funds amid a recessionary economy.

But Bowser mostly embraced the Fenty mantle, saying she shares his penchant for quick action but would be more focused on tackling issues of economic inequality. “Now we’re at a point in our city . . . that we need to look at everybody that was left behind in that process, and our prosperity now allows us to do that,” she said.

Later, Bowser was noncommittal on whether she would retain Schools Chancellor Kaya Henderson, saying there were “a lot of things that I would want to discuss with her” before asking her to stay on.

Evans took Bowser to task for that, citing chronic turnover among the school system’s managers. “We cannot have another school superintendent,” he said. “If you’re not willing to keep Kaya, you shouldn’t be mayor.”

During a discussion of housing issues, Gray criticized Bowser for opposing a proposal to house homeless families in an unused senior home in her ward. Bowser brushed off the critique, saying she was more focused on finding permanent homes for families rather than shelter rooms.

Wells, meanwhile, focused most of his attacks on Gray and Evans, eschewing attacks on Bowser even as polls show her emerging as the favored candidate of anti-Gray voters. Asked which candidate she would most likely support if she weren’t in the race, Bowser said she’d consider Wells. But Wells did not return the favor, referring to Bowser as a “status quo” candidate.

Asked whether he has a path to victory, Wells said that “it’s a volatile race” and that he still could win. In a message to supporters sent earlier in the day, he made it clear that he will not drop out in the final days of the race.

“I’ve often been lobbied to sacrifice my principles and to support something I don’t believe in,” Wells wrote in the mass e-mail. “Well, I haven’t done it on Council and I won’t do it now.”

Evans, who had 6 percent support in the Post poll, also said Wednesday that he had no plans to leave the race. “We’re on the rise,” he said. “It’s unfortunate the way this race is being characterized. It’s ‘Vote for Vince Gray’ or ‘Vote for somebody against Vince Gray,’ and that should not be the way it is. It should be, vote for the best candidate.”