Rep. Jim Matheson, seen as the Democratic front-runner if he chose to run for governor or the U.S. Senate next year, announced Wednesday that he instead will seek a sixth House term in 2010.

"I made the decision in terms of what I think is best for my family and best in terms of serving my constituents," Matheson told The Salt Lake Tribune .

As a member of the House Energy and Commerce Committee, Matheson said he is in a position rare for a Utah representative. "I'm in the thick of a number of issues, and I think it's really important for Utah to have a voice on those."

He said taking on a statewide race also would have been challenging for his family. The Mathesons have two children, ages 7 and 3.

Matheson was his party's most promising hope to win its first statewide race since 1996. The focus, at least for the governor's race, now shifts to two-term Salt Lake County Mayor Peter Corroon, who says he is weighing his options.

Matheson, a member of the moderate Blue Dog Democratic caucus, who has bucked his party recently on health-care reform and climate change, had steadily tightened his grip on what once was a Republican-leaning district, trouncing his GOP opponent in his last election by nearly 30 percentage points.

The inroads he made in Republican districts and his prodigious fundraising -- he had more than $1 million in the bank as of his last campaign report -- had prompted speculation he would challenge U.S. Sen. Bob Bennett or chase the governor's seat, a position his late father, Scott Matheson Sr., Utah last's Democratic chief executive, held from 1977 to 1985.

The national Democratic Party had encouraged him to run for either of the statewide races, Matheson said, and he had been weighing the decision for some time. But Wednesday afternoon, he said he made a handful of calls -- including contacting Bennett and Corroon -- to notify them of his decision.

"I wanted to make sure that others had a chance to make a decision to get into the race on the Democratic side," he said. "I don't want to string this out, particularly if I'm not doing it, putting whoever else gets in at a disadvantage with short notice."

Utah Republican Party Chairman Dave Hansen, who had predicted publicly that Matheson would run for Senate, said the announcement was unexpected.

"I really am surprised he made this announcement this early," Hansen said. "That really doesn't change our plans at all. We still fully intend to run strong, aggressive races for governor, the Senate and the 2nd Congressional District ... and be victorious for all of them."

In his statement, Matheson noted he is not closing the door to a future bid for statewide office, and he will closely follow the redistricting process after the 2010 Census.

Businessman Sam Granato is seeking the Democratic Senate nomination. Utah has not elected a Democratic senator since 1970.

Corroon, who becomes the Democrats' top prospect for governor, said Matheson's decision makes the race for the Statehouse "interesting." He said he does not want to lose focus on county issues, but Matheson's absence makes for "an interesting opportunity for a Democrat in the state of Utah."

A grass-roots movement launched on Facebook to draft Corroon for governor has more than 1,000 members -- even Corroon is following the Web site -- though he has been reluctant to make any commitments.

"I'm happy where I am," he said. "It's obviously an opportunity to consider, but I haven't made any decisions."

Corroon, who has ruled out a third term as county mayor, said he would not have considered the race had Matheson jumped in.

"I respect Congressman Matheson and would never consider running in a race that he was running for," he said. "I always defer to him as a candidate."

Corroon was re-elected as mayor of the state's most populous county by a 2-to-1 margin last November and could retain his seat through 2012 -- even if he lost a governor's bid.

Salt Lake County Councilman Joe Hatch described Corroon as the clear Democratic front-runner now in the governor's race, saying the popular mayor "is going to be very, very competitive."

The real test for Democrats, Hatch said, will be in Davis and Weber counties, where Corroon would be wise to focus his attention.

In addition to Corroon, Utah Democratic Party Chairman Wayne Holland said there are a few other potential candidates for governor, but he would not name them.

"There's a lot of excitement about the potential of a Corroon gubernatorial candidacy," Holland said. "Peter has shown he's a very effective straight shooter in Salt Lake County."

Kelly Patterson, director of the Center for the Study of Elections and Democracy at Brigham Young University, said Matheson's decision makes it tougher for Democrats in Utah and easier for the Republicans in the statewide contests.

"It removes a person from consideration," he said, "who has all that experience as a candidate, has good name recognition, and there just aren't many of those for Democrats."

Patterson said Matheson has become a player in key issues, including the health-care debate, and that might be hard to give up, especially since "statewide office, no matter how you slice it, is still pretty difficult for a Democrat."

A spokesman for Lt. Gov. Gary Herbert, who is expected to become Utah's governor next week, after the U.S. Senate confirms Gov. Jon Huntsman Jr. as ambassador to China, declined to comment on Matheson's decision.

Holland says he still expects the gubernatorial race to draw national attention since Herbert will have inherited the seat rather than been elected to it. "For all intents and purposes it's an open seat."

Jim Bennett, Bennett's son and campaign manager for the senator's re-election bid, said Matheson called the senator Wednesday afternoon to inform him of his decision. But, Jim Bennett said, the campaign hadn't been looking ahead to a potential race against Matheson.

"Right now," he said, "we're focused on the campaign ahead of us and that is the battle for the Republican nomination."

gehrke@sltrib.com

Tribune reporter Jeremiah Stettler contributed to this report.