The crowd had just begun to gather in the crisp autumn sunlight, beneath the red, blue and yellow pennants strung across 29th and O streets NW. They were browsing about the tables of quaint hand-made knick-knacks and moist and fluffy home-backed pastries, while a 1923 carnival organ, complete with a thumping bass drum and flapping cymbal, piped out "Georgie Girl."

But already , Republican Arthur Fletcher was through pressing the flesh at the 6th Annual Georgetown Community Festival. He left, taking his campaign for mayor to an even smaller-but in his opinion, more important-audience on the other side of town.

Half an hour later, Fletcher was sitting board room of a bland brick building on the corner of 3rd and L streets NE that houses the offices of the Capitol Cab Cooperative Association.

Fletcher, with the help of a friend, was talking fast and at times, talking tough, making his pitch to a couple of cabbies whose political support he considers essential to winning the Nov. 7 general election, in which he faces Democrat Marion Barry and two others.

"My father was on this board for 27 years," said former cab driver Lewis Dobbs, who was acting as Fletcher's advance man. "I know the problems we've had in this very board room. I know Arthur well enough to know that he won't come up here with no jive-time promises."

Then Fletcher talked about his own beginnings in Kansas, where he grew up, he said, because, "My daddy was a buffalo soldier, in the 9th Cavalry.

"I helped to start a black cab company myself, in 1949, in Topeka, Kansas," Fletcher said. "It lasted about as long as a snowball in hell."

And at another point, stressing the importance of creating wider job opportunities for minorities (as he said he did while serving as an assistant secretary of labor in the Nixon administration) Fletcher again drew on his own experiences.

"Hell," he said, "I went back to carrying ice after I finished playing professional football not because I wasn't educated, but because I was black."

Cab driver Bernard Jefferson, wearing dark glasses and a blue jacket with "Jeff" embroidered on his chest, seemed a little skeptical of Fletcher's promises. "Are you aware of who runs the District, sir?" Jefferson asked. "I don't think it's the mayor, sir."

"That's the same as when I was at the Labor Department," Fletcher came back. "You know who runs the Labor Department? The AFL-CIO."

The Capitol Cab board, which strongly supported Mayor Walter E. Washington's unsuccessful candidacy in the Sept. 12 primary election, is not expected to make an endorsement untill later this week. But one-on-one sessions with cab drivers were a top priority item foe Fletcher yesterday as he attempted to nail down supporters early.

Democrat Barry, who won his party's close primary by about 1,500 votes, enters the race against Fletcher with city Democrats still somewhat divided. And the 53-year-old Fletcher sees that as an opportunity to make unroads into traditionally Democratic groups, especially those who supported Washington. The cab drivers fall into that category.

In the past, District cab drivers have distributed Washington's campaign literature and ferried some of his voters to the polls as well as cast their own ballots for him. With only one of every 11 city voters a registered Republican, the drivers could give a vital boost to Fletcher, who is running for public office here for the first time.

The cab drivers are among the staunch Washington supporters that some city political observers believe so dislike Barry that they are almost among several cab drivers interviewed yesterday, all of whom had talked with Fletcher, there were no decided choices.

Fletcher's basic campaign pitch is that he has 30 years of experience in government and is more qualified than Barry "to run a billion dollar business, which the city government is."

He is also urging those he meets to watch the joint appearances he and Barry are to make on television. Fletcher, who has been hard-pressed for campaign cash, expects to score political points during the debates.

Both Jefferson and Capitol Cab board member Walter Martin, who listened attentively to Fletcher, said their minds were not made up. "What I've seen here doesn't make me say I'll endorse him," Martin said. I've seen a lot of good talkers in my day."

Out in the parking lot, where a group of cabbies had gathered around the back of a white station wagered of which Charles Burgess was selling fresh greens, William Best talked with Fletcher for several minutes.

"I live in Anacostia. I wanted to know what he was going to do about problems over there," Best said after Fletcher had gone to visit another cab office. "He didn't say nothing, really." He just said he was going to have these workshops or something...."want a realistic approach, not just promises."

The other two candidates in the race for mayor are Susan Pennington of the U.S. Labor Party and Gloza E. Scott, an independent.