A group of black-rights activists sued the city of Annapolis in Baltimore federal court today, charging that the state capital's recently redrawn councilmanic ward boundaries violate the Voting Rights Act.

The suit, which lawyers said is the first brought by private citizens against a Maryland subdivision under the 1965 law, alleges that the redistricting plan adopted Dec. 18 by the mayor and city council "fragments and splits up black population concentrations and dilutes black voting strength."

"I know the effect . . . would be to disenfranchise the black community," said Carl O. Snowden, a longtime civil rights activist here who initiated the suit.

Snowden was joined in the class-action suit by the Anne Arundel Coalition of Tenants, a tenants' rights organization that he heads, and three Annapolis women who previously have joined him in other legal battles: Elizamae Robinson, Martha Wood and Ida Simms.

They are asking the court to throw out the adopted plan and permanently block the city from implementing it. If their case is not tried by September, when the first primary under the new plan is to be held, they said they will seek a temporary injunction to block the election.

Blacks comprise 35 percent of the city's 31,740 residents, but the eight-person council has only one black member. Mayor Richard L. Hillman, who is elected at large, is white. The lawsuit alleges that the newly redrawn plan further hinders a black's chances to win city office because it gives blacks a majority in only one ward, rather than in two under the former ward boundaries.

Such a change results in a "retrogression of the voting strength of minorities in violation of the Voting Rights Act," said Frank R. Parker, an attorney with the Lawyers' Committee for Civil Rights Under Law, who cited a series of Supreme Court and lower court rulings in the last decade.

The committee and private attorney C. Christopher Brown are representing Snowden and the others without charge.

Alderman Brad Davidson, who wrote the council-approved plan, defended his version today as the one that is "the most equitable, does the least damage to existing neighborhoods and offers the strongest possibility of a second black alderman on the council."

Davidson said the plan's creation of a ward with no incumbent and a 48 percent black population on the edge of downtown Annapolis could make possible the election of a second black to the council.

A heavy concentration of blacks in one area of Annapolis made the creation of additional black dominated wards impossible without gerrymandering, he said.

Brown said that a fair redistricting plan would have created three wards with black majorities where a black could at least have an opportunity to be elected. Historically, no black has been elected to the Annapolis city council from a white dominated ward, Snowden said.

A biracial citizen commission recommended an alternative redistricting plan to give blacks a majority population in three wards, to reflect their percentage of the city's population, but it was rejected by the council. Snowden sat on that committee.

Under 1982 amendments to the Voting Rights Act, plaintiffs need only prove that the effect of the redistricting is discriminatory, not that there was any intent to discriminate, said Parker.

Last year, Parker's committee handled 26 voting rights suits throughout the country. All of them were resolved in favor of the complainants, he said.