ALBANY — A victory by the Republican today in the Long Island state Senate race may tempt that body’s GOP majority leader, Joseph Bruno, to encourage one or two of his colleagues to retire from the Senate well in advance of the 2008 election in an attempt to take advantage of the party’s traditional edge in special elections.

Nassau County voters in the 7th Senate district head to the polls today for a special election that has become a proxy battle between Mr. Bruno and Governor Spitzer for control of the Senate, the last bastion of Republican power in state government.

Political observers say the race, which pits a Democratic county legislator, Craig Johnson, against the Republican county clerk, Maureen O’Connell, is too close to call. Republican strategists say they expect the outcome of the contest to have a major influence on Mr. Bruno’s strategy for maintaining control of the Senate. If Republicans come out on top and overcome the financial and political support Mr. Spitzer has given to Mr. Johnson, Mr. Bruno will be further inclined to initiate more special elections as a way to replace aging members of his conference through a process that may serve to his advantage, according to the strategists.

The Senate leadership has yet to talk openly about replacing any member before the 2008 election. Political consultants to the Senate say a special election would make sense in Republican-heavy districts occupied by aging incumbents. In particular, they point to a Suffolk seat held by Caesar Trunzo, 80, who was absent from Senate sessions all of January after he injured himself in an accident. “I would say Trunzo would be a seat where a special would probably be smart,” a Republican consultant told The New York Sun.

A Republican senator who represents a district in Queens, Serphin Maltese, said the conference would not vacate a seat for political purposes. He did say his members ought to prepare themselves for the possibility of another senator stepping down early by lining up competitive replacements. “I think it’s a possibility that has to be explored,” he said. “In a normal course of governing stewardship, you have to be prepared.” For Republicans, the appeal of a special election has dimmed somewhat since the party lost control of the governorship to a Democrat, Mr. Spitzer. Republicans no longer have control over the timing of the election, whose date is set at the whim of the governor. One major advantage of a special election for Republicans is that they can run a candidate in a more controlled political environment in which voter turnout is usually a deciding factor.

In 2008, legislative races will be swept into the broader dynamic of national races, particularly the presidential contest. A strong performance by a Democratic candidate at the top of the ticket could have a trickle-down effect on other candidates. Last year, Senate Republicans were involved in unusually tight contests, a result that was viewed as a side effect of the Democratic national trend and the popularity of Mr. Spitzer, who won in a landslide.

Another advantage for Republicans is that they can pick a replacement candidate without having to pass over the hurdle of a primary, which avoids the danger of a third party stealing away votes by running a competing candidate.

A special election would also allow Republicans to preemptively secure seats at a time when they still have control of the majority. If Democrats make gains in the Senate in 2008, Republicans may find it more difficult to raise money from donors.

A spokesman for Mr. Bruno did not respond to a request for comment.

For now, all eyes are on today’s election, which many perceive as a referendum on Mr. Bruno’s future as leader of the Senate and a test of the political reach of Mr. Spitzer, who has been more involved in this contest than previous governors have been in legislative races in recent memory. Democrats are hoping that a victory today will prove to be a tipping point in their battle to take over the Senate, which Republicans hold by three seats.

Mr. Spitzer called a special election after he tapped an incumbent Nassau Republican senator, Michael Balboni, to be his homeland security chief. Mr. Balboni originally won his Senate seat in a special election.

The five-week campaign to decide who represents a district in northwest Nassau has taken on the grandeur of a statewide campaign. The two sides were on track to break spending records for a legislative race in New York. Early on, Mr. Spitzer led the way by headlining a $25,000-a-head party fundraiser in Manhattan, while Mayor Bloomberg donated $75,000 to the Republican state party. Yesterday, two major presidential contenders, Senator Clinton and Mayor Giuliani, swooped in to lend their star power on behalf of their respective parties’ candidates.

Mrs. Clinton addressed supporters of Mr. Johnson at a banquet hall in Elmont, while Mr. Giuliani appeared with Ms. O’Connell at a Long Island Rail Road station in Floral Park.