Art Fletcher was on the small, red-carpeted stage in the stucco-walled basement of Shiloh Baptist Church. He was strolling back and forth, talking loud, clear and forceful. He was leaning his 6-foot-4-inch frame toward the six dozen people in the audience and being his own cheerleader, remarking, "Let me say that again" whenever he thought he had a good line.

Fletcher knew that Marion Barry, his Democratic opponent in Tuesday's election for mayor, was likely to call him a "stranger" in the city when Barry spoke later to the political forum. "So Fletcher, a one-time professional football player, apparently figured that the best defense was a good offense.

"If I were not from outside this community, I would not be what I am," Fletcher said, "I as advising governors when I was 31 years old in 1954. You were not doing that here then. I was running a highway department in the state of Kansas in 1955."

Later, in 1972, FLetcher said, he had served as executive director of United Negro College Fund. "I wasn't on the payroll," he said. "I was making the payroll. Let me say that again I wasn't on the payroll. I was making the payroll."

Throughout nearly two months of campaigning since winning the Sept. 12 primary. Republican Fletcher has to describe his past and to argue his case that his management experience and business contacts make him the most qualified candidate for mayor.

He raised five children alone for several years after the early death of his first wife.He went from near-welfare poverty to assistant secretary of labor in less than five years. He took the political point for the Nixon administration's controversial "Philadelphia plan" for affirmative action hiring in the construction trades. He helped to integrate the Baltimore Colts football team and the Pasco, Wash, City Council, and he is giving the nation's capital its first credible Republican candidate for mayor.

His critics, and a few post associates, contend, however, that Fletcher, a 53-year-old rough and tumble politican, overstates his achievements.

Yesterday, for example, Fletcher was strongly criticizing Barry's tenure as codirector of Pride, Inc., a self-help and job training organization, when a questioner pointed out that the problems he cited occurred after Barry left Pride. Fletcher then asked, "What kind of a system did he leave behind."

Fletcher ran a similar organization, the East Pasco Self-Help Co-op, in 1965. The co-op which trained 380 people, folded in 1971, two years after Fletcher left the state to join the Nixon administration. At its peak, the co-op employed 32 people, according to its last executive director, the Rev. Floyd Bullock.

Still, Fletcher's campaign for mayor is a true phenomenon in the short history of home rule politics in the District, even though in its present state in appears to be only a shadow of what he had predicted to become when he announced his candidacy April 29.

At that time, Fletcher expected thousands of dollars to pour into his campaign coffers from national Republicans interested in seeing him mount a good contest and attract more blacks to the party.

Then, Fletcher talked of campaigning throughout the primary to create issues, build name recognition, nature a political organization and ultimately, stressing his management ability, topple incumbent Walter Washington, whom he considered the likely winner of an intense three-way Democratic primary.

But it did not work that way. Little money came in. The national Republican Party put its emphasis-and money-on congressional gubernatorial elections and not on Arthur Fletcher's campaign. And, Marion Barry, not Walter Washington, won the Democratic primary.

Now, Fletcher expects to finish his campaign having about $50,000. His posters - ranging from red-and-yellow placards like the kind that announce visiting shows at the Capital Centre to two different magenta-and-white editions-were put up late. He has had no television ads. And, his frustrations with the news media reached a point Wednesday where he simply refused to answer questions and told reporters, "Go ahead, write whatever you want."

Some polls taken so far show Fletcher far behind Barry and not making inroads into the ranks of Democrats, who make up nearly 30 percent of the registered voters in the city. Fletcher aides say, however, that their own surveys indicate that the race is much closer, and that the Fletcher campaign is gaining momentum.

But Fletcher has lost before and many of his friends believe that there are other victories he can win Nov. 7.

"Either way, Art Fletcher has demonstrated his commitment to a two-party system and the Republican Party," said Sen. Robert Dole (R-Kam.), a close political associate of Fletcher.

"He can go only one way and that's up. We need forward looking responsible black leadership in the Republican Party."

Lyn Nofziger, director of Citizens for the Republic, a political action group headed by Ronald Reagan, said, "Even if he is not elected, if he runs an effective campaign and if black Republicans say here's a guy we can respect, I really think there a chance we could rally blacks around him."

"He has a chance through this thing to seize the black leadership in the pary," Nofziger said. "And I hope he does that."

Arthur Fletcher declared his candidacy for mayor of Washington on April 29, after moving to the District only three years earlier and registering to vote on Valentine's Day of this year.

The past 10 years of Fletcher's life has been a constant process of reaching for political office. More often than not he has lost the contest, but out of each defeat he has managed scrape a victory of sorts.

The sole electoral victory was on Nov. 7, 1967, when Fletcher got 916 votes to win election to the seven member City Council in Pasco, Wash. (population; 25,000. He used the recognition gained there to grab a spot on the 1968 Republican ticket as a candidate for lieutenant governor. Although he was the only candidate on the slate headed by Gov. Dan Evans to lose, Fletcher won 40 percent of the vote.

That helped to attract attention for the Nixon administration, which was looking for prominent blacks to put in top jobs. In 1969, Fletcher came to Washington as assistant secretary of labor for wage and employment standards, where the Philadelphia plan and other similar affirmative action programs became his major concern.

Organized labor objected stressously to the Philadelphia plan, and eventually the Nixon administration abandoned it. Fletcher left Washington and went to New York to become a member of the American delegation to the United Nations General Assembly in 1971.

He says the move was aimed at giving him international experience so he could return and become an adviser to the president.

Other observers and critics say that the administration, uncomfortable with Fletcher's ambitious and his stance on the Philadelphia plan, had put Fletcher out to pasture.

Fletcher then became executive director of the United Negro College Fund, where under his leadership the fund raised an unprecedented amount of money. But in his 16 months with the fund he had sharp differences with the 40-odd black college presidents whose schools receive money from the fund, especially when he tried to arrange an appearance on behalf of the fund by Vice President Sprio T. Agnew. In April 1973, Fletcher left.

In the five year since, Fletcher has balanced his energies between a sharp stint as an urban affairs assistant to former president Gerald Ford and trying to promote a greater role for blacks - and at times himself in the Republican Party.

Dole said Fletcher has considered running for Congress from th district centered in Topeka, Kan., Fletcher's home state. Last year, Fletcher apparently hoping to capitalize on a split on the Republican National Committee between supporters of Ford and supporters of Ronald Reagan, ran for Republican national chairman. He got 22 of 150 votes cast.