Five rivals for the Democratic nomination in the D.C. mayor's race continued their efforts to win voter support at a Ward 6 endorsing forum last night, but the major excitement of the event came when police evacuated the building because of a bomb scare.

The forum had been under way in the basement of St. Philip's Episcopal Chapel at 1345 U St. SE for about 30 minutes when a man telephoned police and said he had "heard" that a bomb was planted in the building and was set to go off at 9 p.m.

Police arrived at the scene a few minutes later, asked the gathering of about 250 people to leave the basement and then searched the building for about 45 minutes before declaring it safe.

Later, after the forum resumed, the Ward 6 Democrats, a grass-roots party organization that sponsored the forum, voted overwhelmingly to endorse Mayor Marion Barry in the Sept. 14 primary election.

The vote was 110 for Barry, 24 for Patricia Roberts Harris, and 5 for council member Charlene Drew Jarvis (Ward 4). No votes were cast for either council member John Ray (At Large) or physician Morris Harper.

Before the disruption caused by the bomb scare, Harris, a former secretary of health, education and welfare under President Carter, told the audience that if she was elected she would consider implementing a program that would allow children to begin formal instruction in city schools at the age of 3.

Such a program, Harris said, would limit any possible disadvantages in the upbringing of city children that could hamper their later academic development.

"It's something we need to debate in this city because so any children get left behind so early," Harris told a reporter after she had finished her formal presentation.

"So many children are being born to teen-age parents, and those children need added help. But it's a plan that would also be beneficial to the well-to-do. Children who start school earlier stay in school longer."

Currently children in the District may begin kindergarten in public schools at age 5 and are required to start the first grade at the age of 6. The city school system does not now offer prekindergarten classes, but does conduct some day-care sesions for a limited number of children.

Harris said that if she is elected she would not try to implement the program immediately because of the added cost it would place on a financially strapped school system, but would instead undertake a study to see if the cost is justified, and then look for sources to finance it. "It won't be cheap," she said.

Barry refused to comment directly on the Harris proposal, but told a reporter afterward that the city's Department of Human Services already provides 7,000 places in day-care centers for preschool children and that the school system pays for an additional 5,000.

Jarvis also refused to comment on the proposal, but commented to the reporter that another Harris suggestion that would have the city set aside $25 million each year to ensure against a deficit was "unrealistic."

"That proposal shows that she does not understand the state of city finances," Jarvis said. "There are weeks when the city does not have enough cash to meet its payroll. That he is why Mayor Barry has to float all that money."

Barry responded to that by saying that the city has not come close to missing payrolls, but agreed with Jarvis that Harris' proposal is not feasible. Barry said that Congress would take the set-aside money away by deducting that amount from the federal payment.

Harris told the reporter that getting congressional approval for setting the money aside would be her first step in implementing the plan. She said the set-aside would prevent the city from a facing a financial crisis every year.

Ray did not return to the forum after the bomb scare, but in his opening remarks to the gathering, he continued his criticism of the incumbent with the assertion that, under Barry, the District ranked last in the nation in collecting child support payments.

"If that is the kind of leadership this city wants," Ray said, "I say 'God help us,' because we are going down the drain."