Ward 3 candidates for the Democratic D.C. City Council nomination appeared to distance themselves from Mayor Marion Barry last night while competing to come down hardest on developers with major projects planned on upper Wisconsin Avenue.

Speaking at a forum, Ruth Dixon, a political scientist and publisher of a news letter about the City Council, labeled as "a big lie . . . character assasination . . . a smear" charges that she has been influenced by developers because they have contributed to her campaign.

Mark Plotkin, a candidate who has led the criticism of Dixon for accepting campaign contributions from developers, said at the meeting at the Wisconsin Avenue Baptist Church that "what we need to do is cleanse ourselves of these special interests" and called on Dixon to return the contributions.

James Nathanson, another candidate, suggested that one form of leverage against developers is the city's authority to issue bonds for economic development purposes and said that in the future "if a developer won't cooperate, he won't get his bond issue."

Asked if they would support Barry, each candidate indicated neutrality in the mayoral race. "I do not oppose him, I do not support him," Dixon said. Nathanson seconded the view but said that if elected he would try to work with Barry.

Plotkin said that the mayor had told him last year he might back Plotkin for the council. Plotkin said he replied, "Please don't, I'd like to win."

In answer to a question from the audience of nearly 200, Dixon said one way she would pay for improvements in the public schools would be to reject a proposal for the city to help pay for the acquisition of Antioch Law School by the University of the District of Columbia. She suggested that the city support legal education by providing scholarships "to attend some of the existing good law schools."

The City Council included $1.3 million this year in its fiscal 1987 budget to help UDC acquire Antioch, but since then estimates on how much it would take to run the law school have risen sharply.

Four of the five contenders said they favor raising the drinking age in the District to 21.

"It doesn't make sense to have kids go to Georgetown, tank up and go back to Maryland and Virginia," said candidate Mary Draper Janney, who referred to recent changes in Virginia and Maryland law to raise the drinking age.

Raising the drinking age was opposed only by Jody Pappalardo, a newcomer to the field, who is running on a slate formed by sex entrepreneur Dennis Sobin. She said if people under 21 vote and go to war, they should be able to drink, adding, "How can you do one without the other?"

The Democratic primary is Sept. 9.