Three weeks after taking office, Governor Spitzer is moving quickly to consolidate power in Albany, aiming for a stronger hold on the Legislature than his predecessors, George Pataki and Mario Cuomo, ever had.

After telling New Yorkers in his State of the State address that “division has kept us from moving forward,” Mr. Spitzer is giving an early indication that he intends to replace the “three men in a room” culture of Albany that has become synonymous with gridlock and backroom dealing with “one man in a room.”

Since assuming the governorship, Mr. Spitzer has sought to exert control over the process of selecting the next comptroller, all but declared war on the Republican majority in the Senate, and reportedly began a push to put three ethics and lobbying commissions, including the body that oversees the Legislature, under the umbrella of one agency.

Mr. Spitzer has not been successful on every front. The governor backed away from his demand that the comptroller be a financial expert outside of the Assembly, consenting to the creation of a three-member screening panel that would seem to preserve Speaker Sheldon Silver’s dominance over the process.

But his aggressive efforts have surprised some Albany veterans, who are accustomed to a power structure in which budgets and laws are hammered out by the governor, the speaker, and the majority leader.

“Eliot is a political animal. Anybody who expected he would come to Albany and stop playing politics … was mistaken,” a source close to Mr. Spitzer said.

The most striking difference between the governor’s tactics and those of his predecessors has emerged in Mr. Spitzer’s battle to seize a Senate seat in Nassau County and set in motion a historic Democratic takeover of the Republican-controlled Senate.

Mr. Spitzer put the seat up for grabs when he lured away its popular Republican incumbent, Michael Balboni, who joined the administration as homeland security chief. In the past couple of weeks, the governor has thrown his political muscle, his fund-raising network, and campaign staff behind the campaign of the Democrats’ candidate in the February special election, Craig Johnson, a member of the Nassau County legislature. The actions have turned the five-week race into a referendum on Mr. Spitzer’s governing agenda and on the political future of the Republican Senate leader, Joseph Bruno. Mr. Spitzer has tapped his campaign manager, Ryan Toohey, to run Mr. Johnson’s campaign operations, sources said. The governor on Thursday evening headlined a $25,000-a-person Democratic Party fund-raising dinner at the Manhattan home of developer Henry Elghanayan, an event that raised more than $250,000 for Mr. Johnson’s campaign.

Mr. Spitzer spoke on Mr. Johnson’s behalf in a television ad, and the governor’s was featured in a campaign mailer that compared Messrs. Spitzer and Johnson to the Lone Ranger and Tonto, according to the Albany Times-Union.

The governor, whose first executive budget is due February 1, also plans to take time out of his schedule to campaign with Mr. Johnson at least twice more before the election, a source said.

Political strategists say the race is too close to call, although one private poll reportedly shows Mr. Johnson’s opponent with a slight lead. While Mr. Johnson has Mr. Spitzer vouching for his credentials, his opponent, Maureen O’Connell, a registered nurse, lawyer, and former assemblywoman, is better known in the county.

Democrats are hoping that a Republican defeat would prove to be a tipping point, prompting other Republicans to defect or seek jobs in the Spitzer administration. Senate Democrats say that if they gain control of the house, they plan to execute Mr. Spitzer’s agenda.

“Clearly, if the Democrats take the Senate … I’m going to back Eliot’s proposals to the hilt,” a state senator who represents the Bronx, Jeff Klein, who was recently appointed deputy minority leader, said.

Republicans in particular say they are taken aback by Mr. Spitzer’s involvement in the race, which stands in contrast to Messrs. Pataki and Cuomo, who seldom played a major role in legislative races.

“I’m utterly and completely surprised,” the chairman of the Republican Party, Joseph Mondello, told The New York Sun. “It’s obviously a power grab and nobody can tell me anything different. … You’re basically talking about government by day and politics by night.” After the Democrats’ sweep in the November election, Mr. Bruno installed Mr. Mondello, who is also the county chairman of Nassau, as state party leader, with the expectation that Mr. Mondello would begin to rebuild the GOP infrastructure. A loss in the special election on his home turf would be a humiliating defeat for Mr. Mondello and for Mr. Bruno, who is already weakened by a federal investigation into his outside business interests.

Mr. Mondello cast himself as the underdog in the race. “I don’t think we can compete with them financially. They used to call us a machine, but we’re fighting in a completely Democratic state,” he said. Asked about the political consequences of losing, he said, “I’m not going to lie and say it’s not going to hurt us. But is it the end? No, this is a cyclical business.”