Democrats trying to loosen Republican control of the state Senate won a big victory in the Bronx last night when Assemblyman Jeffrey Klein defeated Stephen Kaufman in the state’s hardest fought primary.

With 87% of the ballots counted, Mr. Klein was leading 58% to 35%. Mr. Kaufman, also an assemblyman, was also losing the Republican primary to retired New York City detective John Fleming 57% to 43%.

This sets up a three-way race in the general election, with Mr. Kaufman running on the Independence and Conservative party lines.

The results were a setback for Senate Republicans, who had supported Mr. Kaufman in the expectation that he would join their 37-24 majority if elected.

Their battle for the Democratic nomination was the hardest-fought primary in the state, with both sides spending hundreds of thousands of dollars.

Across New York City, there were primary battles for five seats in the U.S. House of Representatives, eight seats in the state Senate, 17 seats in the Assembly, and half a dozens seats on the Civil Court. In most cases, incumbents easily defeated their intra-party challengers.

Although voting yesterday by Democratic Party members will likely determine the ultimate winners in many of the races, turnout was low. At P.S. 293 on Cobble Hill, only 16 voters had cast ballots as of 6:30 last night, according to poll worker Maria Maldonado.

“It’s horrible,” Ms. Maldonado said. “I’ve worked at other primaries. It’s always low, but I don’t know how to explain this.”

In one of the hottest contests, Representative Major Owens of Brooklyn, a 22-year incumbent, won the Democratic primary against two members of the City Council, Yvette Clarke and Tracy Boyland, and a college professor, Gabriel Pearse.

Mr. Owens, whose district stretches from Brownsville to Park Slope, has said this will be his last race.

“It’s knowledge, experience, and know-how,” he said. “When you go looking for a doctor or a lawyer, you don’t want someone just out of school.”

In another hard-fought Brooklyn race, Assemblywoman Adele Cohen won a Democratic primary against challenger Inna Kaminsky. With all precincts reporting, Ms. Cohen had 59% to 41% for Ms. Kaminsky.

The Brooklyn Democratic Party, under fire for how it has picked judges in the past, refrained from endorsing judicial candidates this year, resulting in an unusually crowded field of 14 candidates.

Eight of the candidates were vying for three countywide seats and six were in the running for two district spots on the bench.

Though the party as a whole did not back anyone, its embattled chairman, Clarence Norman, came out in support of Housing Court Judge Johnny Lee Baynes, former New York City Housing lawyer Harley Diamond, and Brooklyn prosecutor Evelyn LaPorte.

Many have questioned the stability of the Brooklyn political machine in light of the recent scandals, involving both Mr. Norman, who easily won another nomination last night, and state Supreme Court Justice Gerald Garson, who is accused of accepting bribes.

That “chaos,” some say, will mean trouble lobbying for Brooklyn resources without a stronger and united front.

“There is all kinds of warfare going on in the borough. That kind of activity makes Brooklyn look weak,” said political analyst Hank Sheinkopf. “No matter what the outcome in the primaries, the party is weaker in the borough.”

Party officials acknowledge the divisions, but say the organization is resilient and is still strong. They also deny that Brooklyn will be shortchanged because of those fractures.

“Brooklyn cannot and will not be ignored,” party spokesman Bob Liff said. “Are there challenges along the way? Of course there are. But this is politics. Politics is all about middles.”

For some, the stumping, or at least the endorsements from large newspapers and other candidates, seemed to have worked. Several people interviewed outside a polling site in Cobble Hill were savvy on even judicial candidates.

Cobble Hill resident, Eva Vauchee, said that while the races often get overlooked, “these In the 28th state Senate District, including parts of Manhattan and the Bronx, Councilman Jose Serrano was leading against a former assemblyman, Nelson Denis, and a teacher, Augustin Estrada, for the Democratic nomination to challenge Senator Olga Mendez, a Republican who switched from the Democratic Party two years ago.

In a Republican primary on Staten Island, 24-year incumbent Assemblyman Robert Straniere lost to a challenger supported by GOP leaders, Vincent Ignizio, 1,269-1,672. A third candidate endorsed by the Conservative Party, Mario Bruno Jr., received 1,035 votes.

In Queens, state Senator John Sabini was facing a tight race in the 13th district against fellow Democrat Luis Rosero. Freshman Assemblyman Barry Grodenchik, in a three-way primary, was in danger of being upset by challenger Jimmy Meng. If elected, Mr. Meng would be the first Asian-American to serve in the state Legislature.

Brooklyn judges are so disgusting that I wanted to vote.”

Several primaries outside New York City took on potential statewide significance.

In Nassau County, Assemblyman David Sidikman was fending off a challenge by a fellow Democrat, Charles Lavine, who was running with the support of the county executive, Thomas Suozzi. Mr. Suozzi is trying to organize the ouster of Mr. Sidikman and a Senate Republican, Carl Marcellino, as a gesture of protest against the state Legislature, which he blames for making decisions that drive up local taxes.

In the Syracuse area, Senator Nancy Lorraine Hoffmann was holding off a similar anti-Albany campaign by a fellow Republican, Thomas Dadey, who had the support of local GOP leaders. In early returns, Ms. Hoffmann was leading with 54% of the vote.

Political observers said the low turnout was no surprise. “A September primary, the same week that school starts? It’s almost like New York was going out of its way to suppress turnout,” said a professor at Columbia University’s School of International & Public Affairs, Steven Cohen.