ALBANY – Promising to shake up the state Capitol in the same way he has shaken up Wall Street, Attorney General Eliot Spitzer formally announced yesterday that he is running for governor.

Republicans – testing what could become the theme of their counterattack – immediately tried to turn Mr. Spitzer’s record against him, branding him a “job killer” who has damaged the state’s economy with his celebrated lawsuits.

“He’s made a lot of enemies with his job as an attorney general, and it provides a good opportunity for us,” the chairman of the Republican State Committee, Stephen Minarik, said. “In a broad sense he’s been a job-killer with the anti-business positions he’s taken.”

With a statement posted on the Internet and phone calls to supporters and the press, Mr. Spitzer confirmed what has become increasingly obvious in recent months: “I will run for governor of New York in 2006.”

The 45-year-old Democrat, whose crusades against corruption and fraud in the business world have made him internationally famous, is the clear frontrunner for his party’s nomination now that Senator Schumer has announced his intention to stay in Washington. Many of Mr. Spitzer’s supporters portray him as a shoo-in to replace Governor Pataki, a three-term Republican.

In his announcement, Mr. Spitzer portrayed state government as the latest corrupt institution he intends to clean up.

“I want to fix what’s broken,” he said. “It’s what I do best. I bring people together whether they like it or not and we tackle complex problems – not with Band-Aid solutions, but with major reform and real change. We did it in the financial industry and other sectors and we can do it in government.”

In his six years as attorney general, Mr. Spitzer, a former criminal prosecutor, has launched a series of high-profile investigations and lawsuits against investment bankers, mutual fund companies, and major insurers. In each case he alleged that widespread industry practices amounted to fraud against clients and customers. The targets of these cases, in settlements with Mr. Spitzer’s office and other regulators, generally agreed to change their practices and accept substantial penalties.

Mr. Spitzer has argued that his enforcement efforts are ultimately good for business, because they reassure consumers that the companies they deal with are treating them fairly. Some business officials have publicly endorsed this view. Others, however, privately fault Mr. Spitzer for twisting long-accepted practices into crimes and giving business officials another reason to shy away from New York.

“The only sound we might hear from them is the sound of moving desks and moving feet, going across to New Jersey,” Assemblyman Patrick Manning, a Republican from the Hudson Valley, said. “A large corporation just wants a fair shake and doesn’t want a shakedown.”

“The line of attack would be: Has Eliot Spitzer cost jobs with his overzealous prosecution of industry?” a Republican political consultant, Brendan Quinn, said yesterday.

A Democratic strategist, Hank Sheinkopf, called this “a ridiculous argument.”

“This is pulling at straws,” Mr. Sheinkopf said. “They’re going to come up with anything they can, because they don’t have anybody on the bench to take on the most prominent attorney general probably in history. They’re going to say anything and do anything.”

As if anticipating this line of attack, Mr. Spitzer emphasized that he will focus on improving the economy as governor. “Right now, New York government is all about partisanship and gridlock,” he said. “We’re not doing the things we need to do to generate good paying jobs, safe neighborhoods, and excellent school. … I’ll bring new energy and resolve to the task of transforming state government and turning around the state economy.”

Another GOP consultant, Bill O’Reilly, said it would be a mistake to attack Mr. Spitzer for crusading on behalf of average consumers and investors.

“Any objective person would have to say that Wall Street needed greater scrutiny,” Mr. O’Reilly said. “I think he should be commended for that,and anybody that tries to turn that into a negative probably won’t get very far with it.”

“Anyone who runs against him is going to have to have their own clear vision for the state,” Mr. O’Reilly said. “I don’t think snapping at his heels is the way to take him down.”

Mr. Pataki welcomed Mr. Spitzer into the race but reiterated that he has not decided whether he will seek a fourth term or not.

“I believe in the Democratic system,” he said. “The more the merrier.”

“I hope we can continue to concentrate on governing and moving the state forward,” he added. “The elections are two years away.”

If Mr. Pataki chooses not to run, it is unclear who would get the GOP nomination in 2006. Republicans see Mayor Giuliani as a formidable candidate, and perhaps their best chance to beat Mr. Spitzer, but he is widely expected to stay out of the race and run for president in 2008. Other Republicans who are considering the race include Mr. Pataki’s secretary of state, Randy Daniels, and a state senator from Nassau County, Michael Balboni.

Mr. Minarik said Republicans have other lines of attack against Mr. Spitzer, such as faulting him for avoiding taking clear positions on controversial issues.

“The strategy for beating Eliot Spitzer is to inform people about what he stands for – except we don’t know what he stands for,” he said.

A prominent member of the Conservative Party who was once an appointee of Mr. Pataki, George Marlin, said none of the potential Republican candidates has much of a chance.