When all the bad-mouthing and loud-talking at forums is over and Mayor Marion Barry is making his closing statement, giving his audience his best sell, this is the big stick he picks up:

"When you hear people saying they can do a better job as mayor you should ask them what they are going to do specifically," he said at a recent senior citizens' forum. "You'll hear some proposals from some of my opponents, but from others you'll get nothing but criticism of me without saying what she would do."

The not-so-subtle point is that Barry's leading opponent in the polls, former Carter administration cabinet member Patricia Roberts Harris, had not issued any policy statements or program proposals in her three-month-old campaign until last week when she came out with a paper on how a Mayor Harris would combat crime.

And although Barry has attacked Harris for not saying what she would do, he too has made no statements on what he would do to make the city a better place in the next four years.

The crime rate in the city, for example, has climbed by about 20 percent in the last three years, but Barry still has not come up with any specifics on how he would better handle the city's crime problem should he win a second term.

"We'll be putting out some proposals soon," Barry said in an interview three weeks ago. "We're going to do that."

One of the reasons Barry has been in no hurry to produce specifics on the issues is that his opponents have been content to lash out at him, saying that he has to run on his record in office.

"Now, the mayor, the mayor has to run on the record he has built up over the last four years," said John Ray at another forum. "We all know what that record is and that's why we need a new mayor."

"He ought to hold himself to the same standard he requries of other candidates," said Charlene Drew Jarvis, the Ward 4 council member who is running for mayor. "Look at his record. Marion Barry has really only been mayor for the last few months. Before that I don't know what he was doing. But some of the things he is accomplishing now proves that he could have done so much more earlier that he hasn't done."

But Barry, disavowing much of his own record, regularly tells audiences that he has now learned how to be mayor after years of trouble with water bills, complaints about rude city employes, continued poor conditions in public housing and a sticky financicial crisis.

Barry tells the voters that in the last year of his administration he now has the kind of experience that his opponents lack. Barry explains to voters that it would be best to reelect him and take advantage of his experience.

"I'm running on all four years," Barry said at a recent forum sponsored by the Washington Association of Black Journalists. But then he added, "I'm saying we're getting started on the right road now. I'm running on my record for all four years but I don't want anyone to forget what we've been doing in the last year. We've got a record, we have programs in place now, we know what has to be done now."

Barry has made special efforts to remind voters of why he should be reelected. His administration created the Mayor's Gold Card program, a discount card issued to senior citizens. There is a new campaign to promote the city, called "Washington is a Capital City." Both are advertised on radio and television. Just before the mayor announced for reelection, there was a new anti-crime effort; last week, there was the opening of new housing for senior citizens, built with funds from Asbury Methodist Church and federal funds obtained while Walter Washington was mayor.

This last-minute flurry of activity raises the question of whether all the sins of an administation should be forgiven on the principle that the mayor needed a learning phase and it would be too costly to shift leadership just when the mayor claims to have gained the experience to do a good job.

Or should voters look at the record for what it is and decide, like a teacher whose favorite student has failed a test, unpleasant as it may be, to give a failing grade?

When the incumbent cites accomplishments, what he most often says is that being mayor is a tough job, one that he came to at a difficult time when the city had financial problems. He cites some recent projects: keeping the streets clean, improving the administration of the summer jobs program, having the city's financial books audited last year.

As for his first 2 1/2 years in office, Barry told reporters recently that when he came into office he did not realize all the problems and did not get much done.

"I find it incredible that he is in any way enjoying any respect on the question of what he promised in order to become mayor," said Sharon Dixon, Harris' campaign manager.

"By his own admission, when he came into office he didn't know what to do. He says he didn't know what was there, like the financial problems, but he was chairman of the City Council Finance and Revenue Committee. He should have known. . . . . Now that he's getting around to promising to do what he didn't do he says he wants people to believe him."