The district of Columbia Board of Elections and Ethics has adopted a far-reaching rule that would require the mayor and other top city officials to vacate their offices temporarily if they formally are accused of conflicts of interest.

Under the rule, which is to be published officially tomorrow and is to take effect Dec. 23, any affected official would restored to office only after his case is legally concluded.

Shari B. Kharasch. who will leave office next week as chairman of the elections board, said the rule is intended to put certain top-ranking officials - notably the mayor and the chairman and members of the City Council - under conflict rules similar to those applying to subordinate city officials.

The rule was drafted chiefly by Jeanus B. Parks Jr., a board member and law professor at Howard University. It will take effect shortly before mayor-elect Marion Barry and a new council take office Jan. 2.

Winfred R. Mundle, the elections board's former general counsel denounced the new rule in a legal opinion that war prepared shortly before he left that job two weeks ago and was distributed at yesterday's board meeting. Mundle said the new rule applies stricter standards to top officials than do other rules to subordinates.

Under D.C. law, a subordinate official, such as a department head is required only "to remove himself from influence over actions and decisions on the matter" they may involve a conflict of interest.

The new rule says that affected officials, "specifically including the mayor and chairman of the council," are so influential in city operations "that temporary removal from office is the only means of assuring the public is a conflict-free exercise of the powers of the office . . ."

Temporary removal of a top official would be triggered by a letter of notification of the charges from either the elections board or the city's director of campaign finance, a powerful official who works closely with the elections boards.

D.C. law defines conflicts chiefly as an official's outside financial interests that could affect the conduct of office.

Since the city's home rule government went into effect in 1975, no elective official has ever been formally accused of a conflict of interest.

However, had the broad terms of the new rule been in effect, it might have applied in 1976 and 1977 to Sterling Tucker, who leaves office Jan. 2 as council chairman.

It was disclosed at the time that a New York-based foundation had established a $25,000 trust fund of his children. After the fund was dissolved, the elections board cleared Tucker of any wrongdoing, Tucker never stepped aside from his council post.

Under one interpretation of the new rule, Barry might be put into the position of creating a conflict for himself soon after taking office as mayor.

Barry will be faced with a need to nominate a successor to Kharash as chairman of the three-member elections board and to the retired Carl McIntyre as campaign finance director.

However, one source pointed out, Barry's finances in his 1976 race for a council seat still are under review, and either or both of the new mayor's nominees might be called upon to participate in a final decision. That situation would be averted if the case is closed before Jan. 2.

The new conflict rule was presented to the elections board last Wednesday, and adopted without substantial discussion or debate by a unanimous vote of Kharasch, Parks and James T. Denson.

Copies of the rule were distributed at yesterday's meeting, and the text will be published tomorrow in the D.C. Register, the city's compendium of legal notices. It will go into effect automatically unless the board reverses itself.