Flushed with cash, Republicans in the New York State Senate are expected to hold on to their majority over the Democrats in tomorrow’s election and may even pick up a seat.

Democrats would need to pick up four seats to take over the Senate, which has been in Republican hands since 1939 with the exception of one term in the 1960s. But both Democrats and Republicans say only one incumbent Republican, Nicholas Spano, of the 35th Senate district in Westchester, is in serious danger of defeat.

The likely outcome means that the next year’s governor will once again deal with a divided legislature. In New York, where Democrats outnumber Republicans by a 5 to 3 margin, the ideological differences between the two parties in the Legislature are less pronounced than on the national level. Traditionally, the Senate has been more geared toward the interests of upstate and Long Island voters and the Assembly has been a creature of New York City. On crime, taxes, and education, the Republican Senate has served as a check on some of the Assembly’s leftward tendencies.

A Republican source speaking on background said the party’s internal polling is showing Mr. Spano leading his Democratic opponent, Andrea Stewart-Cousins, by five to 10 percentage points.

“We are cautiously optimistic,” said the executive director of the Senate Republican Campaign Committee, Edward Lurie, who is a top contender to replace Stephen Minarik as chairman of the state Republican Party. “It always depends on who comes out to vote.”

Voter turnout is the wild card in the Senate races, say both parties. Democrats are hoping that the popularity of gubernatorial candidate Eliot Spitzer and Senator Clinton will trickle down the ticket, driving up turnout in their own party and keeping more Republicans home on Election Day.

But Senate Republicans have two key advantages: money and the power of incumbency. They are outpacing Senate Democrats in fundraising by a huge margin and are insulated by gerrymandered districts.

In the last week and a half, the Senate Republican Campaign Committee has raised more than $1 million, about 20 times more money than Republican candidate for governor, John Faso, has taken in during the same period.

Senate Democrats are projecting an upset and are directing committee

dollars and deploying get-out-the vote troops behind Ms. Stewart-Cousins, a county legislator from Yonkers who lost to Mr. Spano by 18 votes in 2004. Mr. Spitzer and Mrs. Clinton have campaigned with her in recent weeks, and the candidate also appeared in an ad with the attorney general that was produced by the Spitzer team.

Chastened by the 2004 squeaker, Mr. Spano has leaned left politically, sponsoring dozens of labor friendly pieces of legislation to get in the good graces of the Working Families Party.

The incoming leader of the Senate minority, Malcolm Smith, who is taking the reins from lieutenant governor candidate David Paterson, said his party’s strategy is spread over three terms beginning in 2004, when the party narrowed the gap by picking up three seats. He said Democrats are aiming to take one seat away from Republicans in this election and three more in 2008.

Beyond the battleground of the Spano-Stewart-Cousins rematch, both parties say a potential for an upset exists in a handful of other races. Democrats say Ulster County legislator Susan Zimet has an outside chance of beating the Republican incumbent John Bonacic. The Spitzer campaign has deployed a staffer to assist Ms. Zimet’s campaign. Republicans are eager to retake the 49th district and are pouring money into assemblyman Jeff Brown’s campaign against the one-term incumbent, David Valesky.