JEFFERSON CITY, Mo. -- Secretary of State Robin Carnahan said Wednesday that she will not run for governor in 2008, squelching speculation of a Democratic primary showdown against Attorney General Jay Nixon.

Carnahan, the daughter of the late governor Mel Carnahan and former Sen. Jean Carnahan, told The Associated Press she had seriously considered a gubernatorial bid but will instead seek re-election as secretary of state.

She cited personal reasons. Carnahan, 45, got engaged on Christmas to her boyfriend of almost four years, Juan Carlos-Antolinez, and she recently completed successful treatment for breast cancer.

"One of the things this year has taught me is to have a little more patience," Carnahan said in a telephone interview. "I've decided I'm going to spend a little more time having some balance in my life."

Republican Gov. Matt Blunt has not declared whether he will seek re-election but has been steadily raising money. Blunt's campaign had $1.8 million on hand as of the end of September. The next quarterly campaign finance reports are due Jan. 15.

Nixon, a four-term attorney general, reorganized his campaign committee in November 2005 to enter the governor's race. His most recent report showed about $918,000 on hand.

Speculation of a Carnahan gubernatorial bid had increased in recent weeks as she sought advice about a potential run.

Ultimately, Carnahan said, she decided that a highly competitive gubernatorial primary and general election would have been far more demanding -- both personally and on her family -- than a re-election bid as secretary of state.

Carnahan said she instead will support Nixon in his gubernatorial campaign. No other potential Democratic candidates have surfaced.

Her decision to skip the 2008 governor's race was not based on political concerns, said Carnahan political consultant and family friend Saul Shorr, of Philadelphia. He said private polls conducted for others had shown Carnahan with a significant advantage over Nixon in a potential Democratic primary.

Nixon's campaign office referred questions to treasurer Craig Hosmer, who said he was not aware of any political polling on a potential matchup of Nixon and Carnahan but added that her support of Nixon showed the Democratic party is unified.

Hosmer described Carnahan and Nixon as "key allies" in a campaign that would likely pit Nixon against Blunt.

Blunt campaign spokeswoman Bekah Cooper had no direct comment about Carnahan's decision.

"The governor is focused on the legislative session that's coming up and continuing the work of the people," she said. "He's not really thinking about an election that's two years away."

Carnahan, an attorney, was elected secretary of state in 2004 in her first campaign for public office. Her brother, Rep. Russ Carnahan, D-St. Louis, is an attorney who first was elected to Congress that same year. Another brother, Tom Carnahan, also is an attorney and is currently developing commercial wind farm projects in Missouri.

Their father, brother Randy, and Mel Carnahan's longtime aide, Chris Sifford, were killed in an October 2000 plane crash while Gov. Mel Carnahan was campaigning for the U.S. Senate seat held by Republican John Ashcroft.

Mel Carnahan won the election anyway and his wife, Jean Carnahan, was appointed to the Senate seat, which she lost in a special 2002 election to Republican Jim Talent.