A Democratic assemblyman says Sheldon Silver should step down as Assembly speaker, warning his colleagues that Albany’s most powerful Democrat would sabotage the governing plans of the party’s front-runner in the gubernatorial race.

Airing a rare note of dissent from the Democratic conference of the Assembly, Mark Schroeder, a first-term lawmaker of Buffalo, sent a letter on Tuesday to all 102 of his Democratic colleagues urging them to consider electing a new speaker. He compared the candidate, Eliot Spitzer, to past governors of New York such as Grover Cleveland and William Sulzer, who entered office vowing to shake up the system only to be thwarted by the incumbent legislative leaders.

“If history is any guide, however, popular reform governors like Spitzer are often obstructed from carrying out the reforms that the electorate has so strongly supported,” Mr. Schroeder wrote.”Unfortunately, unlike their role in the election of the governor, the people have little influence on the election of the two legislative leaders. The power lies directly with us.”

Mr. Spitzer this year criticized the size of the budget and pressed for legislation, such as a DNA criminal database, that Mr. Silver was at first reluctant to support. If the attorney general has plans to depose Mr. Silver if he’s elected governor, he’s not discussing them publicly. A spokeswoman for his campaign, Christine Anderson, said via e-mail, “Eliot has always had a good working relationship with the Speaker and hopes to work with him in state government from day one to achieve real reform.”

Democratic lawmakers are expected to elect Mr. Silver to a seventh two-year term as speaker when they meet in December before the start of next year’s session. The New York press has long portrayed Mr. Silver, a trial lawyer from the Lower East Side, as one of the villains of Albany, painting him as a politician who is more responsive to special interests than to voters, and one who legislates behind closed doors.

Democratic lawmakers say in interviews that Mr. Silver has well served their collective interests and has helped expand the party’s majority. The speaker’s leadership has not been threatened since 2000, when a Democratic assemblyman, Michael Bragman, staged a failed coup. He was stripped of his office and leadership post and resigned in a year.

Mr. Schroeder told The New York Sun he has yet to receive a response from any of the lawmakers. “Today’s a lonely day for somebody like me,” he said. “The only phone calls I get are people in my district.”

In his letter of reply, Mr. Silver stressed what he described as his smooth relationship with Mr. Spitzer and his confidence that the Democratic conference would work in tandem with Mr. Spitzer toward achieving Democratic goals. He noted that he was among the first elected officials to endorse Mr. Spitzer’s candidacy in 2004.

Mr. Schroeder was elected in 2004 when public sentiment against Albany was at a high pitch. Lawmakers missed their deadline for passing a budget for the 20th consecutive year, and a think tank had published a report naming New York’s Legislature as the most dysfunctional in the nation.

Mr. Schroeder told voters that unless Mr. Silver pledged to pass an on-time budget he wouldn’t support him as speaker. Instead of voting against Mr. Silver in the 2004 conference election, he boycotted the meeting at which his colleagues voted unanimously to keep Mr. Silver as their leader.

Tensions flared between Messrs. Schroeder and Silver early in the Buffalo lawmaker’s first term of office. He accused the speaker of punishing him for his dissent by denying him space for a district office. Mr. Silver said at the time that he rejected the request for an office because the space was shared with a civic organization and a private business, whose rent the speaker said should not be subsidized by the state. Mr. Schroeder said yesterday that the dispute was resolved and had been due to a “miscommunication.”