Patricia Roberts Harris is leading incumbent Marion Barry at this early stage of the mayor's race, according to a new Associated Press-WRC-TV poll. Of those interviewed, 39 percent said they would vote for Harris while 28 percent said they would vote for Barry.

Harris is slightly ahead of Barry among blacks interviewed--36 percent to 34 percent--but she holds a striking 44 percent to 19 percent lead among whites interviewed, according to the poll results.

A total of 405 persons who said they were Democrats and planned to vote in the Sept. 14 Democratic primary were interviewed by telephone last Wednesday and Thursday, the pollsters said. The poll has a margin for error of six percentage points, according to a spokesman for WRC.

None of the other three major mayoral candidates received support of more than 7 percent, suggesting that at this point, before the campaign begins in earnest, it is a two-way race.

The first candidate-preference question in the poll did not mention the names of those running, but simply asked, "Whom would you most like to see elected mayor of the District of Columbia." In response to that question, Barry and Harris each drew 27 percent. The largest single response was "not sure," with 36 percent. No other candidate got more than 3 percent when that question was asked that way.

Then interviewers listed the names of the candidates, with Harris drawing 39 percent and Barry 28 percent. At-large council member Betty Ann Kane was closest to the two leaders, but far behind them, with 7 percent.

At-large council member John Ray was preferred by 5 percent and Ward Four council member Charlene Drew Jarvis by 4 percent. Seventeen percent said they were undecided or would vote for someone who has not announced.

Barry declined though a spokeswoman to comment on the poll. His opponents in the race said the poll showed that Barry has surprisingly little support for an incumbent mayor.

"Marion has a very low amount of support for an incumbent, but I'm not surprised," said Ray. "All the polls done last year by people thinking about running showed he had a very low level of support for an incumbent. That's why you have so many people running."

Barry's poor showing among whites was particularly striking. In the 1978 primary Barry won Ward 3--the only ward in the city that has a predominantly white population--with 47 percent of the vote. Sterling Tucker, the former City Council chairman, and then-mayor Walter Washington got 34 percent and 18 percent of the Ward 3 vote respectivley.

But according to the AP-WRC poll, Barry would now lose to Harris among white voters citywide by 44 percent to 19 percent, with Ray getting 6 percent, Jarvis 1 percent, and Kane, the only white candidate in the race, winning 13 percent.

The poll also showed that those interviewed, by a wide margin, said a candidate's race was not an important factor. A total of 89 percent said it made no difference whether the mayor of Washington was black or white.

"I think the people who were responsible for putting him Barry into office are the people most disappointed with him," said Kane. "The hopes he raised and the promises he made have not been fulfilled . . . He was the man who promised to make the government efficient and courteous, and my files are filled with complaints from people who are still put on hold for hours and still can't get an answer from a city employe."

Harris, who the poll says has the best chance of defeating Barry, said she interpreted the poll results as showing that many people have not yet begun to concentrate on the race. But when they are forced to make a decision, they turn it into a two-person contest.

"I'm certainly heartened that the poll shows the voters feel I am the best person to be mayor," Harris said. "But you know that the only poll that counts is on the 14th of September. I'm still an underdog running against an incumbent, but the poll does make it clear that it is a two-person race . . . just two people have a chance of winning this campaign, and it's going to be a very hard-fought campaign."

Interviewers also asked participants in the poll whether they would vote for incumbent Arrington Dixon or Council member David Clarke (D-Ward 1) in the race for City Council chairman if the primary were held today. Forty-five percent said they would vote for Dixon, 26 percent for Clarke; 29 percent said they were unsure.