The D.C. Board of Elections and Ethics voted preliminarily yesterday to remove mayoral candidate Dr. Morris Harper from the Sept. 14 Democratic primary ballot, after a sampling of his nominating petitions indicated he lacked the required signatures of 2,000 registered voters.

Board Chairman Albert J. Beveridge III said Harper's petitions--along with those of eight other candidates for city offices, which also did not meet the requirements--would be rechecked by Friday before a final vote is taken.

However, sources close to the board said that the elections office has reviewed virtually all of the 2,341 signatures turned in by Harper and that it is unlikely he will be certified for the ballot. Elections officials said candidates usually must collect three signatures for every two they hope to certify.

"I stand behind all the signatures on my petitions," Harper told a reporter last night. "We are happy to be challenged because every signature there is a good one. They are valid, and we are ready for a challenge."

It was the latest in a series of setbacks that Harper, a 34-year-old physician, has faced in his first attempt to win public office here. The elections board initially declined to accept the nominating petitions now being questioned, and agreed to take them only after Harper demonstrated that incorrect information from an elections worker had caused him to file the petitions after the deadline.

The elections board has scheduled an Aug. 12 hearing on a report by the Office of Campaign Finance into allegations that Harper inflated the amount of campaign contributions he had reported in an June 10 filing. Several persons listed as contributors told The Washington Post that they either had not contributed to the campaign at all or had given less than what Harper's reports showed.

The other eight candidates--who, like Harper, will have four days to challenge the board's action if the rejections of their petitions are confirmed--include Democratic City Council at-large candidates Patricia Wells and Osie L. Thorpe; Republicans John West and Viola E. James, who are vying to challenge D.C. Del. Walter E. Fauntroy; Ward 1 Democratic council contenders Ester L. McCain Jr.and Calvin O. Wingfield; and Ward 5 Democratic council candidates Richard S. Lee and Rufus T. Langford.

Under a change in the law last spring, the board was required for the first time to certify that each candidate, based on a scientific sampling, had submitted petitions that were 95 percent accurate. Candidate petitions are used in the District in lieu of qualifying fees.

Board chairman Beveridge, noting the certifying procedure proved to be cumbersome and interferred with other election preparations now under way, urged the City Council to go back to the old system in which it was up to individuals or candidates to challenge the petitions.

"It is a bad law and it should be repealed," Beveridge said.