ALBANY — A busy day for state politics provided Governor Spitzer with a valuable political lesson: He has more influence over the electorate than over lawmakers.

The governor helped Democrats pull within two seats of taking over the state Senate with yesterday’s victory of his hand-picked candidate, Craig Johnson, in the high-profile Long Island special election to fill a vacant seat. With 100% of precincts reporting, Mr. Johnson was leading Maureen O’Connell by 26,452 votes to 22,929.

Assuming Mr. Johnson’s victory is not challenged by Mrs. O’Connell, Mr. Spitzer will have delivered the seat to Democrats virtually single-handedly. He opened it by appointing the incumbent, Republican Michael Balboni, to be his homeland security chief. His political operation then oversaw Mr. Johnson’s campaign, picking staff, organizing fund-raisers, and crafting a message aligned with Mr. Spitzer’s governing agenda.

As usually is the case with special elections, voter turnout was low, with about 20% of registered voters braving the sub-freezing temperatures to go to the polls.

The governor’s victory in Nassau, however, was overshadowed by developments in Albany, where Assembly Democrats exited a private conference meeting poised to elect one of their own members to be comptroller — despite the governor’s strenuous objections to such a move.

Mr. Spitzer was heading for a political defeat that in some ways resembled a setback he experienced early in his first term as attorney general, when a judge threw out his public nuisance lawsuit against the gun industry. In both cases, Mr. Spitzer appeared to overplay his hand, overestimating his ability to shame a target into compliance.

In an extraordinary last-minute appeal, Mr. Spitzer delivered a two-page letter to all legislators, warning them of the consequences of not selecting a candidate designated by a special screening panel supported by Mr. Spitzer. The governor said it would be a “huge mistake” for lawmakers to choose a legislator to succeed convicted felon Alan Hevesi as the state’s chief fiscal officer.

“You are telling the public that only legislators are eligible to serve as Comptroller, and that merit, independence, and qualifications do not matter,” Mr. Spitzer stated.

The strategy seemed to be inspired by Mr. Spitzer’s successful playbook as attorney general, where shame was an important weapon in his arsenal in his investigations and settlements with Wall Street companies. This time, the strategy may have backfired on the governor.

“Even my mother and father don’t talk to me like that,” said Democratic assemblyman Keith Wright, who represents Harlem, said, referring to Mr. Spitzer’s letter. “Talking about that there will be consequences. I mean, come on.”

Although Assembly Democrats, the most powerful bloc in the Legislature, remained bitterly divided over which of their members they plan to elect comptroller in a joint-house vote as early as today, they came out confident that they wouldn’t choose any of Mr. Spitzer’s choices for the job.

Mr. Spitzer is accusing the Democrats of breaking their agreement to choose a comptroller from a pool of candidates selected by a bipartisan screening panel composed of two former state comptrollers and a former city comptroller.

Democrats regretted entering into the agreement after the panel returned with three finalists, none of whom were members of the Assembly. The speaker of the Assembly, Sheldon Silver, who represents Lower Manhattan, said the panel relinquished its legitimacy by not putting forward a larger pool of candidates and by excluding lawmakers, who represented a third of the 18 applicants.

“He relies on a process that was flawed. In his heart, he knows it was flawed,” Mr. Silver said yesterday. “The governor has to respect that there may be some times when people disagree with him, period.” Mr. Silver met with the governor in Mr. Spitzer’s second-floor office for more than an hour but came to no agreement.

Although they were united against the governor’s involvement in the process, Assembly Democrats left yesterday without settling on a candidate. Mr. Silver scheduled a meeting for Democrats to discuss the issue at 12 p.m. today and a meeting of the full Legislature has been called for 2 p.m. today, when the candidate is expected to be voted on.

In recent days, Mr. Silver has been trying to line up support behind Thomas DiNapoli, a low-key Long Island lawmaker known for his loyalty to the speaker. At the urging of the speaker, county chairmen from the Bronx, Brooklyn, and Queens have been pushing their local lawmakers to get behind Mr. DiNapoli.

The other leading candidate was Richard Brodsky, a Democrat of Westchester, who said his numbers were strong but had shrunken somewhat since the county chairmen began a push for Mr. DiNapoli.

Some Democrats privately grumbled whether it was appropriate to protest Mr. Spitzer’s attempt to influence the vote but allow interference by county bosses, who are powerful players in legislative races.

The internecine battles could help to allow Mr. Spitzer to walk away from the comptroller battle with public support behind him. Mr. Spitzer used his voter popularity to his advantage in the Long Island race, where the Republican candidate, Mrs. O’Connell, the clerk of Nassau County, lost to a younger and lesser well-known opponent, Mr. Johnson, a county legislator from Port Washington who was recruited by the governor and whose campaign was managed and funded by Mr. Spitzer’s political operation. Mr. Johnson is the first Democrat to be elected state senator in Long Island in many years.

Mr. Johnson’s victory is likely to embolden Mr. Spitzer’s efforts to lead a historic Democratic takeover of the Senate.

The defeat of Mrs. O’Connell, a registered nurse-turned-lawyer who served several terms in the Assembly, places Senate majority leader Joseph Bruno’s control over his conference in a perilous state. Senate Democrats, who are led by Malcolm Smith, now need to seize only two more seats to take over the Senate and complete the party’s monopoly of power in the state.

Before the election, there was speculation that dissatisfied Republican senators, fearful of becoming marginalized, would be tempted to defect to the Democrats if Mr. Bruno failed to gain back the Long Island seat.

It wasn’t only Mr. Bruno who was under pressure to win. The special election was the first major test of his hand picked party leader, Joseph Mondello, a Nassau political boss whose local influence on the island, especially in Hempstead, was supposed to be a bulwark against Democratic advances in the crucial power base of Long Island. Blame is also likely to be pointed at Senator Dean Skelos, a Nassau Republican and a potential successor to Mr. Bruno.

The race was the most expensive legislative race in state history, with combined spending of both candidates reportedly surpassing $5 million. The high stakes could also be measured in the star power that was drawn into the campaign. Two of the nation’s leading presidential contenders, Senator Clinton and Mayor Giuliani, dropped in this week to make appearances on behalf of their party’s respective candidates.