Four years after spending more than $60 million of his own money to get elected to the Senate, Democrat Jon S. Corzine (search) announced Thursday that he is running for governor in 2005.

The former investment banker, whose political intentions have been widely reported in recent days, becomes the first Democrat to officially enter the race. Polls have shown Corzine would be the early front-runner.

"I believe I can do more for the state of New Jersey and its citizens as governor," the freshman senator said. He said he left private life for the Senate to press for better health care, education and government, and pledged to continue those battles.

Corzine is entering the race nearly four months after Gov. James E. McGreevey (search), a Democrat, announced his resignation and disclosed that he had had a gay affair.

Corzine, 57, was elected to the Senate in 2000, the first try for public office for a man who made a fortune as head of investment bank Goldman Sachs.

He was only two years into his Senate term when the party tapped him to head the Democratic Senatorial Campaign Committee, a job that involves extensive fund raising and recruitment of candidates.

Corzine's possible Democratic rivals include Richard J. Codey (search), the Senate president who is serving out the final year of McGreevey's term.

The Republicans who have announced their candidacies include businessman Doug Forrester (search), who lost a Senate race to Democrat Frank Lautenberg in 2002, and Bret Schundler (search), who lost the 2001 governor's race to McGreevey.

The winner of the governor's race will appoint someone to serve out the final year of Corzine's Senate term.

David Rebovich, director of the Rider Institute for New Jersey Politics, said Corzine must convincingly explain his decision to leave the Senate so soon after the 2000 campaign. Otherwise, Rebovich said, "he will be subject to the criticism that he's a bored billionaire with no power in Washington and he just wants to come back to Jersey."