When Mayor Marion Barry appeared recently at a meeting of area black dentists, it could not be said that most of those in the audience were old Barry supporters. During the close campaign for the Democratic nomination for mayor, may of the city's medical professionals preferred Barry's opponents -- Walter E. Washington or Sterling Tucker.

Unfortunately, perhaps, for Barry's efforts to unite previously divided key elements of the community, when Barry left the meeting there still were some significant disbelievers in that audience.

It was not, some said afterward, the result of old feelings dying hard. Rather, the new mayor seemed to have a knack for saying a few wrong things -- like addressing the physicians and dentists as "Doc" during a question-and-answer session -- and, strangely for Barry, not being as up on the issues as he could have been.

There was loud applause for many of Barry's statements -- his praise for the black medical schools from which many of the country's black physicians and dentists have graduated, his call for a larger federal payment and his pledge to get rid of deadwood and discourtesy at city hall. The applause was similar to the generally optimistic and anxious response he receives in various parts of the city.

But on the medical issues -- the ones in which many of the dentists said they were most interested -- there was only a polite reception. There was, in fact, no applause when Barry announced his plan to increase the number of dentists practicing in the District by giving financial assistance to dental students who agree to work in the District after graduation.

The reason for that silence, some dentists said afterward, was a feeling that Barry had missed the boat. He had failed to understand his own transition team's report, which had noted that the attitude of D.C. government, as much as anything else, discourages dentists from practicing in the city, they said.

"You've got plenty of dentists who want to practice here," one society member said afterward. "You don't have to get new dentists to come into the city. Just give the old ones some reasons to stay."

"That's a waste of manpower," another said of the proposal. "The resources and the manpower are already here."

Dentists complain that the city's Medicaid system pays too little, takes too long to issue checks and has arbitrary methods of deciding which dentists will be investigated for possible overpayments. Barry acknowledged that the dental portion of the Medicaid program was "not as strong as it should be." That drew applause. But it was only a passing reference; the details would have to await further task force studies.

One dentist who worked on Barry's transition task force complained privately that the new mayor has simply not placed a top priority on health care matters, even though the Department of Human Resources, which administers most public health care programs, is the city government's largest agency.

Barry has appointed no general assistant for health matters. He has announced his intention to launch a strong offensive to lower the city's infant mortality rate. But that came, the task force member said, only after a front-page article in The Washington Post underscored the problem.

Moreover, noted one dentists, Barry, who during his campaign promised to fire several city department heads he considered incompetent, has said nothing about removing anyone in DHR, including Director Albert P. Russo and Russo's top health adviser, William Washington, who was quoted in the Post article as saying he did not know enough about infant mortality to discuss the subject with a reporter. "That was appalling," the task force member said.

"Somehow you get the feeling that Marion is already too much obligated to other people to make health care a priority," the dentist said. "Everybody here seems to be taking a wait-and-see attitude."

Barry used his speech to the dental group to defend his Jan. 8 criticism of Cardozo High School as a place where noise in the halls and drug use in the bathrooms hindered the educational process. Students and faculty members at the school had complained that the statements unfairly disregarded many of the schools academic achievements.

"I've learned long ago," Barry told the dentists, without specific references to the school, "that you can't learn when there's all kinds of noise and you're high on marijuana.

"I'm not gonna talk about what you do at home. That's private. A number of my friends smoke marijuana. Privately. At home."

Barry is on record as favoring decriminalization of marijuana.