With several competitive Democratic contests in Brooklyn’s heavily black City Council districts and ho-hum races in predominantly white districts, some analysts and political power brokers are anticipating a possible spike in the percentage of black turnout across the borough in September’s primary election. That could provide a lift to a state senator, John Sampson, who is the only black candidate remaining in the borough’s heated four-way district attorney race.

The four-term incumbent district attorney, Charles Hynes, is facing his fiercest re-election fight since he took office in 1990. In addition to Mr. Sampson, the field of challengers includes the former chief of the state attorney general Eliot Spitzer’s anti-corruption division, Mark Peters, and a former Koch administration official, Arnold Kriss. Earlier this week, another black candidate, the election lawyer Paul Wooten, who was expected to siphon some black votes from Mr. Sampson, withdrew from the race. No district attorney of New York City has been defeated for re-election in at least a half-century. This September, however, a state assemblyman from Boro Park, Dov Hikind, predicted, “It’s going to be a battle.”

The district attorney’s race is not the only hotly contested primary in Brooklyn. More than a dozen candidates are seeking the council seat from mostly black Ocean Hill and Brownsville that is currently held by a Democrat, Tracy Boyland, who is leaving office as a result of term limits. Meanwhile, five other black incumbents from the borough – Charles Barron, Yvette Clark, Letitia James, Kendall Stewart, and Albert Vann – are facing primary challengers. Although incumbents generally are considered prohibitive favorites, “Even a minor challenger will boost the activity of the one who is challenged, which may boost turnout,” a professor of public affairs at Baruch College, Douglas Muzzio, said.

Meanwhile, six white council members – William de Blasio, Simcha Felder, Vincent Gentile, Michael Nelson, Domenic Recchia, and David Yassky – are running unopposed in September, according to documents from the Board of Elections, while a seventh, Lewis Fidler is expected to face only minimal competition.

The black City Council races “should increase the turnout in the African-American communities,” a black state senator from Brooklyn, Carl Andrews, said. Mr. Hikind made the same point about the contested races. “Clearly, that plays to Sampson’s favor,” the assemblyman, who has yet to endorse a candidate for district attorney, said.

Two council members in majority Hispanic districts, Sara Gonzalez of Sunset Park and Diana Reyna of Bushwick, are also facing competition in the Democratic primary. The other council member from the borough, Erik Martin Dilan, who represents a majority Hispanic district including Cypress Hills, East New York, and Wyckoff Heights, is not facing a September challenger.

A spokesman for Mr. Kriss, one of the white challengers to Mr. Hynes, Brian Krapf, said that if the tight races for the council do boost black turnout, “it might actually help us.” He said Mr. Kriss has been speaking at black churches in the borough “almost every Sunday.”

And a Hynes spokesman, Mortimer Matz, noted that in the 2001 Democratic primary, the D.A. outpolled his lone challenger, a black civil-rights lawyer, Sandra Roper, in all but one assembly district. Even in the heavily black 56th District, Ms. Roper won by fewer than 100 votes.

Meanwhile, in a phone interview with The New York Sun last week, Mr. Peters, the other white challenger, downplayed the potential impact of the contested council primaries in black districts.

“The mayor’s race is what typically gets people to the polls,” the former Spitzer lieutenant said. A professor of political science and sociology at the CUNY Graduate Center, John Mollenkopf, agreed with Mr. Peters’s assessment that spikes in turnout usually stem from the mayoral race at the top of the ballot.

“In 2001, the mayoralty was open and people thought that the Democratic nominee was going to have a real shot,” Mr. Mollenkopf said. With Mayor Bloomberg well ahead of his Democratic rivals in most polls this year, Mr. Mollenkopf said, primary turnout might fall from four years ago.

“And I think that has to help the incumbent in the district attorney’s race,” he said.

According to a former council member from Brooklyn Heights, Kenneth Fisher, however, the presence of two minority candidates on the mayoral ballot – the Manhattan borough president C. Virginia Fields, who is black, and the former Bronx borough president, Fernando Ferrer, who has Puerto Rican origins – could boost turnout in predominantly black precincts.

“In the abstract, given the demographics of Brooklyn and given the fact that the mayoral candidates will be pulling every black voter, that creates a natural base for Sampson,” Mr. Fisher said.

Moreover, he said, “There’s some institutional resentment of Hynes because of his crackdown on corruption.” That was a reference to the district attorney’s continuing investigation of a powerful black state assemblyman from Crown Heights, Clarence Norman. Those factors “would be a concern for Hynes, but for the fact that Hynes has a good record on issues of concern to the black community, going back to the Howard Beach prosecutions,” Mr. Fisher said. In 1986, Governor Cuomo tapped Mr. Hynes to serve as a special prosecutor in the death of a black man who was run over in the Howard Beach section of Queens while fleeing from belligerent young white men who were harassing him. Mr. Hynes secured convictions against three white youths in the case.

Even if the council races do boost turnout in black neighborhoods, Mr. Sampson must court support aggressively from other ethnic groups in Brooklyn, according to a political consultant aligned with the state senator’s campaign, Hank Sheinkopf.

The consultant said Mr. Sampson is eyeing the borough’s chasidic Jewish community, which is concentrated in Mr. Hikind’s district. While Mr. Hikind said the state senator “at this point is not a household name in the Jewish community,” he said Mr. Sampson won kudos from several rabbis for his strong support of Israeli settlers on a visit to the Gaza Strip in May. On the trip, Mr. Sampson, standing next to Mr. Hikind, blasted the Israeli government’s plans to uproot the settlers. Recounting the trip in a phone interview last week, Mr. Hikind said approvingly: “He has guts.”