State Senate Republicans, shaken by an unexpected election loss on Tuesday that put their majority on the edge of extinction, said they are united behind their leader, Joseph Bruno, and vowed to win what they described as a “war” against Governor Spitzer.

The conference’s failure on Tuesday to win an open seat in one of the most Republican districts in the state left the capital in a state of quiet shock, diverting attention away from budget negotiations and to the question of whether Mr. Bruno and his aging colleagues could muster the political strength to recover.

In dramatic fashion, Mr. Bruno yesterday sought to reassure donors and other supporters about the future and quell speculation that he would step down from his leadership post.

After meeting privately with his conference, he gathered Republicans for a press conference during which he portrayed Tuesday’s defeat as an isolated “phenomenon,” and insisted his conference remains loyal to him.

“When this war is over, this conference, which is standing united and tall, we’re going to increase our conference membership after November,” Mr. Bruno said. “This conference is solidly behind me going forward to win this war. … I am, frankly, charged up. I have been knocked down before, and you get up and fight.”

Eliciting applause from his fellow lawmakers, Mr. Bruno pledged that the Republicans would head into the November legislative elections as a united force, accusing the Spitzer administration of spreading rumors that members of his conference are planning to retire early or defect from the party and join the Democrats.

He called the governor’s office and the Senate Democratic conference “the greatest propaganda machine since the Second World War.”

Democrats, who control all four statewide offices and the Assembly, are one seat away from taking over the chamber for the first time since the 1960s after Tuesday’s win by Democrat Darrel Aubertine over Republican William Barclay in a special election held in upstate New York.

The Democratic victory was especially important for Mr. Spitzer, whose power struggle with Republicans has stalled his agenda.

Mr. Bruno said his party is “going to remind the people of this state that Republicans in this conference represent diversity … checks and balance … so you don’t have a bully trying to steam roll over a whole constituency.”

By no accident, Mr. Bruno was flanked by two Republican senators who are most thought to be eying his job, Dean Skelos of Nassau County and Thomas Libous of south-central New York. He invited both to address reporters and declare their support for him.

“We feel a responsibility to this conference, no. 1, to Joe as our leader, but most important to the constituents we represent,” Mr. Skelos said. “This conference is going to win this war.”

In interviews, Republicans acknowledged that their defeat has forced them to reassess strategy. While they said Mr. Aubertine, an affable dairy farmer from Jefferson County, was a naturally stronger candidate than Mr. Barclay, a wealthy lawyer, they also acknowledged that their attack message, which attempted to associate Mr. Aubertine with Mr. Spitzer’s controversial policies, did not resonate with voters.

State Republicans, however, questioned whether the loss reflected a broader problem with the Republican message, which has trended politically leftward under Mr. Bruno’s leadership, a change that some in the party have argued was necessary to survive in a state where Democrats outnumber Republicans by five to three.

“You can’t say you’re for lower taxes and lament every spending cut. You can’t pretend you’re for fiscal responsibility and ignore a $5 billion deficit,” a prominent Republican who asked not to be identified said in an interview.

While Republicans declared their solidarity with Mr. Bruno and expressed confidence in the future of the conference, senior staffers to the majority leader have been eyeing positions outside of state government, a source said.

“It’s going to be a struggle,” a Republican senator of Brooklyn, Martin Golden, said. Mr. Golden, who has strong support within his district, said the conference concluded that a leadership shake-up would only weaken its prospects and that the conference would be better off with a “united force going forward.”

Mr. Spitzer, taking the advice of his senior advisers, passed on chances while talking to reporters to revel in his triumph, sticking to the message that his administration was focused on getting a budget agreement with lawmakers.

Behind the scenes, Mr. Spitzer has been mapping out battle strategy and lining up candidates to take on Republicans in the fall.

Last week, according to a source, the governor in Albany met with Tim Green, a former defensive end for the Atlanta Falcons whom Democrats have tried to recruit to challenge Republican incumbent John DeFrancisco for a Senate seat in Syracuse, a source said. Mr. Green is said to have agreed to run after the governor promised the Democratic Party would finance his campaign.

A spokesman for the Senate Republicans, John McArdle, said the party is counting on support from Republican donors who hadn’t appreciated the threat facing the conference until Tuesday and are now awakened to the prospect of a Democratic monopoly over state government. “That strikes fear in the hearts of many people,” he said.

Sources close to the Republicans said any shakeup in Senate leadership would take place in the next two days, if it were to take place before the November election.

Either way, the prevailing view among Senate Republican supporters was one of pessimism. “It’s a little bit like the Hillary campaign; everything looks good, but the votes are not there. This is not a good time to be a Republican,” a source close to the Republicans said.