Gov. M. Jodi Rell will not seek re-election in 2010, she announced in a surprise press conference Monday evening.

Rell did not give a specific reason for her decision, but she said she wants to focus the rest of her term on the state’s budget. The budget for fiscal year 2010, which passed the Democrat-controlled Connecticut General Assembly in September without Rell’s signature, is already running a deficit, and Rell’s approval ratings have dropped in recent Quinnipiac University polls, one of which will be released today. Three Democratic state senators interviewed said Rell’s decision makes it more likely for a candidate from their party to take control of the governorship in 2010.

“The challenges of the job have been — and continue to be — many, the rewards incalculable,” Rell, who has been governor since 2004, said at the press conference, according to a transcript released by her spokesman Rich Harris. “But at some point, you know inside that it is time to begin a new chapter in life.”

In a statement released Monday, State Senate Minority Leader John McKinney, R-Fairfield, said he thinks Rell led Connecticut through some of its most difficult times and will continue to make “the best decisions” for the state as officials work to close the budget deficit.

And Rob Simmons, a Republican candidate in Connecticut for the U.S. Senate, said in a statement that Rell “earned the admiration and enduring support” of Connecticut residents. Although there has been speculation that Simmons would seek the governorship if Rell were to retire, he will continue to pursue the Senate seat, he said in the statement.

State Sen. Thomas Colapietro, D-Bristol, said he thinks the economy made it difficult for Rell to continue to gain the public’s affection.

“I can imagine she’s just plain tired,” he said.

Rell refused to sign the budget passed by the state legislature in September, saying the budget’s spending cuts were not sufficient as the state faced an $8 billion two-year deficit. The budget became law days later without her explicit consent.

At least five Democrats and one Republican have said they are considering running in the 2010 gubernatorial election. According to the Hartford Courant, Lt. Gov. Michael Fedele, a Republican, told a group of reporters after Rell’s press conference that he plans to seek the governor’s seat and that he will make an official announcement soon. In addition to three other current candidates, Democrat Ned Lamont SOM ’80 announced last week his decision to form an exploratory committee, and Democrat Secretary of the State Susan Bysiewicz ’83 told reporters earlier this year that she hopes to run.

State Sen. Martin Looney, D-New Haven, said Rell’s decision creates an opportunity for Democrats “better than we have had.”

“She would have been a formidable candidate,” he said. “Anyone else [the Republicans] would be likely to nominate would not have been as strong as she would have been.”

Rell came into office in 2004 following a corruption scandal that ensnared former Gov. John G. Rowland, who ultimately resigned that June.

Before she became governor, Rell, 63, was a state representative from Brookfield and the lieutenant governor. She is known for her tough stance on tax increases in Connecticut, where the tax rate is relatively high compared to other states. Historically, her ratings have been abnormally high for a public official, reaching 83 percent in 2005. In September, that number dropped to 59 percent — her lowest ever — but she is still one of the most popular elected officials in the state’s history.

“I came in at a troubling time in our state’s history,” Rell said at the press conference. “We had been through much, and we needed a new start, a renewed sense of faith in public officials and a recommitment to integrity in our government. Working together, we steadied our state and we passed landmark ethics reform and campaign finance reform legislation. I am very, very proud of that.”

She added that she and her husband, Lou, who were both afflicted with cancer during her tenure, are in good health. Rell’s second and third grandchildren were born within the past year.

The Associated Press and Sam Greenberg contributed reporting.