Pondering the latest poll that has Mayor Marion Barry out 13 points ahead of his main rival, Patricia Roberts Harris, I'm reminded of a variation on the old Southern saying, "Every goodbye ain't gone."

In the case of the city's Democratic nomination for mayor, the variation would go, "One poll doesn't end a campaign." A late April poll conducted for the Associated Press and WRC-TV showed Harris leading. The Washington Post poll taken between June 16 and June 22 has Barry leading in seven of the eight wards of the city. These kinds of swings are not unexpected at such an early stage of a campaign.

But this poll does carry some messages.

One message is that Marion Barry has gone a long way toward cleaning up his act and restructuring his image. He is looking better and speaking better, and he's much more acceptable to the ordinary working person who now sees him as a man of the people rather than the old community activist and street dude.

His street-guy manner was an important counterpoint to suit-and-tie Walter Washington in the late l970s. But that image had become counter-productive.

The new and broader support reflects a new pride in Barry and approval of his image. That's important to, say, the hard-working voter in far Northeast who wants her sons to do better in life than she did. Barry's new appearance, better diction and cooler conversation make him a better role model for that voter's teen-aged boy.

Barry also has managed to project himself in a better light to some of the better-educated, upper-middle-class blacks and whites who once complained that he was "gauche."

By contrast, Patricia Harris always has had a strong personal image. She looks and speaks well and carries herself with dignity. Those who objected to her in the poll said they disliked her pride and aggressiveness--and surely there's an element of sexism in that. Similar qualities would be admired in a man.

Harris has a record of holding high office that can be matched by only a handful of people in the country. The poll revealed her strongest claim to fame is her ability and experience at this national level.

But Harris has not been able to convince people what her strong image and national background mean in substantive terms for the people of Washington. Her long-time residence and local connections, even her experience with city problems, are like individual pieces of a puzzle that people don't seem able to fit together in a clear image of how she would fare as mayor of this city.

She still hasn't convinced that God-fearing churchwoman in far Northeast of her genuine interest in her; she still hasn't sold an image with which that woman can identify.

She must therefore build a better case for holding the job.

Incumbent Barry's record, as we know it now, won't dislodge him from City Hall--the city may creak quite a little bit, but it works. We assume that Harris has a program but she hasn't told us what it is.

The voters are wondering if Harris is going to move; they're pondering whether she can do it. At one recent forum, the audience winced during a hostile frontal attack on Barry and grumbled about her lack of specifics about what she would do if she were in his place. She was forced to defend the tone of her criticism: "To attack a record is not to attack a person," she said tartly to one visibly upset Barry supporter.

Although Harris has promised position papers, a platform and a statement of how she intends to accomplish her goals, her strategy may be simply to hold off until later in the campaign. But she can't avoid giving us a program much longer, for if she simply attacks, she comes off negatively and then is read by the voters as hostile.

Maybe the poll that showed Barry way out front will be the dynamite that blows this campaign off dead center. There's still time for Pat Harris to show us her plan as well as her personality.

But as the well-financed and politically skilled incumbent has shown us, it is much easier to restructure an image than it is to build a record.