A confluence of surprising political developments has put the Republican control of the state Senate in real jeopardy for the first time in decades, according to veteran Republican Albany operatives.

The great survivalists of state politics, Senate Republicans and their 78-year-old leader, Joseph Bruno, have a long history of defying the odds and eking out victories in a state where Democrats outnumber Republicans by more than five to three.

The crumbling of Governor Spitzer’s popularity last year brought a fresh sense of hope among Republicans that they would again repel advances by Senate Democrats in this November’s legislative races.

This past month, however, Republicans have suffered a series of setbacks that have sharply increased confidence among Democrats and Mr. Spitzer that their party will imminently take over the chamber, where Republicans lead by 32 seats to 29.

These events include the unexpected retirement of two Republican state senators, a closer-than-expected contest for an open seat, the emergence of a new crop of viable Democratic candidates, and a revived federal investigation of Mr. Bruno.

“Anyone who’s not anxious in this type of climate is not being realistic,” a veteran Republican lobbyist said. “There is more concern than there has ever been before. There has to be concern.”

Lawmakers say the perilous state of the Republican conference has filled the Capitol building with a tension that has overshadowed budget negotiations and other normal legislative business in the early days of the session.

Last year’s profanity-strewn shouting matches between Messrs. Spitzer and Bruno have given way to a quiet entrenchment with few direct encounters.

“Obviously, with the two-vote margin, we’re concerned about any future losses. Just do the math,” a Republican senator of Elmira, George Winner, said.

He said he and his colleagues remain confident, predicting that voters would refuse to hand Mr. Spitzer “unilateral power.”

For Mr. Spitzer, who has openly declared his desire to oust Mr. Bruno and his party from power, the darkening landscape for Republicans is of huge importance for a governorship that has been paralyzed by bitter disputes between his administration and the majority leader.

Owing to his control over his party’s purse strings, Mr. Spitzer wields much influence over the Senate Democratic leadership, which he would expect to unite behind his agenda if they come to power.

For Republicans, the most pressing concern is a February 26 special election in the North Country that was triggered by the retirement of Senator James Wright, who has served since the early 1990s.

The race pits two popular assemblymen against each other: Democrat Darrel Aubertine, a former dairy farmer who has railed against upstate companies that have relocated out of New York despite taking state grants, and Republican Will Barclay, who comes from a well-known political family in Oswego County.

An overwhelmingly Republican seat covering a wide swath of land, the 48th district was assumed to be safely in Republican hands.

Democrats and Republicans interviewed said polling data, which is more unreliable in gauging special elections, is indicating a tight race.

A Democratic win would be traumatic for Republicans and could prompt additional retirements of members, eight of whom are 73 years old or older, or persuade others to abandon the party, Republican and Democratic Albany observers said in interviews.

“There are people who will consider what else they want to do with their lives. It just starts to snowball,” a lobbyist close to the Senate Republicans said.

“If Aubertine wins that seat, it’s a whole other story,” a Republican lobbyist said. “They would be hanging by their nails.”

Another Republican lobbyist interviewed said a loss could even persuade Mr. Bruno, who has served as majority leader since 1995 and has given no indication of retiring, to decide against seeking re-election.

Adding to the uncertainty facing Mr. Bruno are reports this week that federal investigators are examining his relationship with Albany-area unions that invested millions of dollars of pension fund money with a Connecticut investment firm where the majority leader was employed.

A week earlier, Republicans were dealt more bad news when a senator of Erie County, Mary Lou Rath, announced that she would not seek re-election.

A Republican assemblyman, Jim Hayes, whom Mr. Bruno had hoped would compete for the seat in November, surprised many by saying he wasn’t interested and would rather preserve his leadership post in the Democrat-controlled Assembly.

Meanwhile, Democrats are targeting with new intensity Joseph Robach’s 56th district seat, which covers Rochester.

This week, the Democratic town justice of Brighton, Richard Dollinger, who occupied the seat between 1993 and 2002, announced he was resigning and was considering challenging Mr. Robach, a former Democrat.

A competitive race is also emerging in Queens, where Serphin Maltese, who was re-elected by a slight margin in 2006, is expected to face a fierce challenge from a City Council member, Joseph Addabbo.

In recent years, as the Senate Democratic conference has inched closer to the majority, Republicans have intensified fund-raising efforts, recalibrated their positions to appeal to more liberal constituents, and joined forces with organized labor.

Mr. Spitzer’s election in 2006, which brought a Democrat into the governor’s house for the first time in 12 years, provided a new sense of purpose to the Republicans’ struggle, allowing them to cast it as a resistance against one-party control.

A year ago, Mr. Spitzer sought to topple Mr. Bruno’s majority from within. The governor invited members of the senator’s conference to his executive chambers, making individual appeals to them to join his party or his administration.

While the governor made his overtures, Senate Democrats boasted that it was a matter of only days before they took control. Republicans, however, closed ranks behind Mr. Bruno and rebuffed Mr. Spitzer, whose clashes with the Senate leader only drew them closer together.

“I honestly think that very few observers believe that they will pick up any of our seats, and I think there’s very little chance of sustaining all of the seats they’ve got now,” a Democratic senator of Manhattan, Eric Schneiderman, said. “I think the people of New York are moving away from the Republican Party.”