The idea was to put on a luncheon, at the Capitol Hill Club, invite a long list of Republican fat cats and reach into their pockets for $500 checks for Arthur A. Fletcher's D.C. mayoral campign.

So with great expectancy that a single fund-raising event would raise a large sum of money for the former assistant secretary of labor, engraved invitations were sent out saying that William Brock, the Republican national chairman, was inviting the prospective contributors to lunch.

Th reality of yesterday's would-be lunch was something else. The event was canceled last week for lack of interest.

"There was some response, but nowhere near what they'd hoped for," said Paul Hays, the city's Republican party chairman and a Fletcher supporter. "There were very few takers at $500, less than 10."

Peter Teeley, spokesman for the Republican National Committee, said 500 invitations were sent out and that half a dozen said they would come. When the event was canceled, some calls were made notifying the invitees.

But Teeley said that a dozen contributors never got the word and showed up at the club for lunch anyway.

Those contributors and others will get another chance, after the Sept. 12 party primary, assuming Fletcher wins. Teeley said Brock will host a breakfast, but it probably will be for $100 a head this time.

Fletcher is opposed in the primary by Jackson R. Champion, who ran as the party's mayoral candidate in 1974 and received 3,501 votes out of 95,693 cast.

"We decided we'd get a much bigger and better response after the primary," Fletcher said. "The fact that the press is only covering one race [the Democratic mayoral campaign] has been less that helpful. I do have folks asking me if I'm running.

"Campaigning anywhere in the summer is hard," Fletcher said. "Campaigning in the District of Columbia is damned near impossible."

Fletcher has raised $12,158 for his campaign, according to his recent campaign financial report. He said he also has formed an "Art Fletcher's $1,000 Club" with the hope of getting 50 people to contribute that much. He said that so far 25 people around the country have pledged the $1,000 donations and that a few have been sent.

In the meantime, Fletcher said he is campaigning at Subway stops and a variety of candidate forums.