In 2006, New Haven saw a different face of Mayor John DeStefano Jr. — not the exuberant smile he flashed last week when he won his ninth term as mayor, but a defeated grimace as he lost the governorship of Connecticut to incumbent M. Jodi Rell.

Now, with Rell’s announcement Monday that she will not seek reelection, the 2010 gubernatorial race has been blown wide open. But DeStefano will not enter the fray, City Hall spokeswoman Jessica Mayorga said Tuesday.

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The mayor does not plan to run again for governor, she told the News; instead, he intends to focus on school reform in New Haven. But, even if he did run, one political expert and one city official interviewed said DeStefano would be entering an already crowded Democratic field, which includes Ned Lamont SOM ’80 and Secretary of the State Susan Bysiewicz ’83. Board of Aldermen President Carl Goldfield said he thinks the mayor’s attitudes towards his mayoralty have changed since 2006.

Mayorga said DeStefano enjoyed his run for governor in 2006 as he traveled the state talking about the economy and other issues. “But,” she added, “these are challenges that can best be answered through what is being accomplished in New Haven.” DeStefano, who is at the National League of Cities Convention in Texas, could not be reached for comment Tuesday.

DeStefano’s 2006 campaign raised a record $5.6 million and gained the most endorsements of any gubernatorial candidate in the history of the state. He lost by nearly 30 percent of the vote. Still, aldermen and residents said at the time that DeStefano did not pay enough attention to the city while running for state office.

After announcing last week that he would form an exploratory committee to look into running for governor, Lamont praised DeStefano for his decision to stay in New Haven and complete his education reform plans.

“What I see over the last year is that New Haven is at the forefront of education reform,” Lamont said. “The rest of the country is looking at John DeStefano and New Haven.”

The Board of Aldermen approved the city’s teachers’ union contract Thursday, making way for the city to start working on its reform plans, which have been praised by state and national officials. But two aldermen interviewed Thursday, including Ward 5 Alderman Jorge Perez, said elements of the reform process remain to be determined.

Scott McLean, a political analyst for the Quinnipiac University Polling Institute, said if DeStefano did decided to run again, he would be a “long shot.”

“It would be very difficult for him to do that,” McLean said, “given that the Democratic [Party] went with him once and Rell defeated him pretty easily.”

A Quinnipiac University poll released Tuesday found that Bysiewicz would have been the Democratic frontrunner in an election against Rell. (DeStefano was not included in the poll.) But Bysiewicz still trailed Rell by six percentage points.

“[The poll] still shows that Bysiewicz would be the strongest candidate for the Democrats because she’s got the highest favorability rating,” said Douglas Schwartz, director of the poll.

Schwartz added that the Republican Party would be in a better position going into the 2010 gubernatorial election with Rell running.

McLean said that Rell’s decision Monday increases the odds that a Democrat will become the next governor of Connecticut.

But that Democrat will not be DeStefano.