The U.S. District Court ruling that has thrown the Maryland Democratic Party's convention selection rules into disarray is now the basis of a similar complaint by members of D.C.'s Democratic State Committee.

At the center of the Maryland decision, handed down by U.S. District Judge Walter E. Black Jr. late last month, is a national party rule requiring that half of the delegates chosen to attend national conventions be women. Black found that Maryland's execution of the rule -- in which women were listed separately on the ballot and voters were instructed to select an equal number of men and women -- is unconstitutional.

The Maryland matter is still subject to appeal, but some D.C. Democrats are pointing to the Maryland decision to bolster an argument they have been making for years: that similar rules in the District are unfair and unduly restrictive.

"I dispute the whole basis of the thing," said Mark L. Plotkin, a Ward 3 state committee member and unsuccessful 1986 D.C. Council candidate. "Women are very capable of attaining electoral success without this."

Florence Pendleton, an ex-officio state committee member from Ward 5, argues that using sex as a factor to determine who attends conventions is arbitrary and in fact excludes some active Democrats who happen to be men.

"If you've had two male mayors for a period of time, should the next mayor be female?" she said. "If we're going for equalization, let's go all the way. You'll find people saying, 'Next we want five blue-eyed people and five brown-eyed people.' "

The Democratic National Committee and local party leaders defend the use of the equal division rule, which was intended to extend access to the party to women, who are the majority of voters but not among the majority of elected officials.

"We feel that this is going to be a narrow order which only applies to Maryland," said committee spokesman Terry Michael. "We feel confident that as a national party we will be able to implement an equal division requirement."

James M. Christian, chairman of the D.C. Democratic State Committee, said this week that the Maryland ruling has no legal effect on D.C. party rules. But local party lawyers are studying the Maryland ruling anyway, he said, and will report on its status at the party's September meeting.

"The state committee feels that the equal division rule is a valid approach to ensuring representation of women on slates to the national convention," Christian said. "We have supported the Democratic Party's effort to maintain it. But we may very well take a different view once we take a look at the Maryland decision."Eclectic Voter Turnout

The D.C. Board of Elections and Ethics has added a new twist to the mundane process of tabulating election returns: four-color, digitized maps that can show voter turnout at a glance.

The new computer capability is likely to be a boon to candidates for office in the District, who now rely on voluminous lists of voter records to lead them to the wards and precincts where their vote- gathering efforts are most likely to pay off.

"You've heard the old expression that one picture is worth a thousand words," said Robert Jamieson, the elections board's financial manager. "Well, one map is worth 14 printouts."

The maps, which break down into color-coded presentations voter participation as well as such variables as polling place accessibility, are derived from computer software developed for the D.C. Elections Board by Election Data Services, a Washington firm.

Jamieson said that while the public has always had access to all of the information that will be presented in the digitized format, "you don't necessarily understand what you're seeing sometimes. If it's presented on a map, you can begin to analyze where heavy turnout has been and where light turnout has been."

According to the 1986 turnout figures, the highest-voting precincts are in Ward 3 along the Maryland line and in sections of Wards 4 and 5. Most of the remaining Ward 3 precincts are in the next highest-voting category, with 45 to 60 percent of the registered voters casting ballots in November 1986. The lowest-voting precincts were concentrated in Ward 8.