Dorothy Maultsby was about to walk in the door at the Mount Vernon College chapel last week when a supporter of D.C. Democratic mayoral candidate Marion Barry asked her to sign Barry's petition to get on the Sept. 12 primary election ballot.

"But I'm Dorothy Maultsby," protested the retired government management analyst. Undaunted, the perhaps slightly ignorant Barry supporter asked her to sign anyway.

Such ignorance is Maultsby's biggest problem: After all, she, too, is trying to win the Democratic primary race for mayor. But by all tokens, the 51-year-old candidate's campaign is going to be a steep uphill battle at best.

Most politicians and voters throughout the city view the crucial Democratic primary as a three-way struggle among City Councilman Barry, City Council Chairman Sterling Tucker and Mayor Walter E. Washington. A recent Washington Post poll showed those three dividing more than 60 percent of the vote with another 35 percent undecided.

Nonetheless, Maultsby, who registered a scant 1.4 percent in the poll, can be found nearly every day trekking through one neighborhood after another in search of votes and almost every night attending the endless list of debates and speeches community associations throughout the city have already held or are planning.

In appearance after appearance, Maultsby, a retired Department of Health Education and Welfare employe, delights in lumpping her three major opponents in one heap and tarring them all with a single broad stroke.

"We know who caused the inefficiency at the District Building," Maultsby typiccally told a debate audience at Mount Vernon College. "The responsibility rests with the current mayor (Washington), the chairperson of the City Council (Tucker) and the chariperson of the finance and revenue committee (Barry)."

Mautlsby's rhetoric at candidate forums seems always to received politely, but then attention seems to turn quickly back to Barry, Washington and Tucker. During a lengthy question and answer session at the Ward 3 debate at Mount Vernon College, Maultsby and John L. Ray, another mayoral candidate, were asked one question apiece. All the other questions and complaints went to the three major candidates.

Still, Maultsby plunges ahead with a mixture of personal cheerfulness and persistence in the belief that her candidacy is worthwhile and that she will be the next mayor of the District.

Rarely, shesays, does a campaign appearance go by when someone doesn't invite her to speak somewhere else as well.

"I think it's important for (the voters) that there's a choice to make if they want to make it," she said this week. She was campaigning door to door in 90-degree heat, passing out campaign flyers and talking with voters in North Portal Estates, a neighborhood of $100,000 and up homes at the northern tip of the District.

Dressed in a bold, striped multicolored blouse, a denim skirt and sandals, Maultsby hiked from house to house, beads of sweat mounting on her forehead. No one was at home at half the houses. When she did find someone, it was generally an undecided voter, though a few identified themselves either with Washington, Barry or Tucker.

The number of "undecideds" buoyed her spirit. She encouraged these voters to read her campaign flyer and "give me a fair shot."

'Hmmm," she said to herself at one point after talking with an undecided voter, "she hasn't made up her mind. Keep working, Dorothy."

"I'm bringing out the true status of operations in the District" government, says Maultsby, who often cites chapter and verse of the District's misdeeds during the 3 1/2 years Washington has been elected mayor.

Despite Maultsby's assertion that she doesn't think the other candidates "take me lightly," the major contenders generally tend to ignore her charges. She challenged Tucker to a debate this week on whether he's responsible for the District's tenuous financial footing. So far, she said, he has ignored te request.

"We've not paid that much attention to Mrs. Maultsby," Gerald Wallette, Tucker's compaign manager, said recently. "Your asking me about Dorothy Maultsby is the first time I've thought of her in four weeks.

"I've not spent a half hour thinking about her," Barry said.

Barry, however, did not think enough of her stature as a community leader in the Lamond-Riggs neighborhood in Northeast Washington and in other civic activities to ask for her support before she announced her own candidacy.

Maultsby has been involved in a variety of civic and political activities in the District, serving as the chairperson of a citizens committee that successfully opposed construction of the North-Central Freeway several years ago and head of a committee protesting rate increases by the Potamc Electric Power Co.

Because she has not run for elected office before, some people have wondered why Maultsby is starting at the top, rather than running for a City Council seat.

But Maultsby politely rejects such notions, saying, "We need to serve in capacities where we feel comfortable. I do not see the council, and particularly our City Council, as a training ground for mayor. I decided I wanted to go where I could serve best."

So Maultsby continues her campaign with a corps of 106 unpaid volunteers, a campaign treasury of about $2,000 and the praise of people who may in the end not even vote for her.

On her walk in North Portal estates, Peter L. Robinson Jr., a graphics artist, invited Maultsby into his home and gave her a glass of ice water.

After listening to her campaign pitch, he told her that he still was inclined to vote for Tucker but that he'd keep an open mind.

"I think it's good you're running," Robinson said. "You're going to surface some issues. I think you're going to be a worthwhile candidate."