BISMARCK, N.D. (AP) — North Dakota Sen. Byron Dorgan said Wednesday he decided against running for a fourth term because he wanted to pursue other opportunities, not because the prospect of a formidable challenger chased him from the race.

“I actually kind of enjoy competition. It’s one of the things I’ll miss,” the Democrat said of a possible Senate run by Gov. John Hoeven, a three-term Republican who has won his last two races with more than 70 percent of the vote.

Republicans expect Hoeven to run, and recent polls had shown Dorgan trailing in a hypothetical contest. The governor said Wednesday he has thought “seriously” about the race and expects to announce his plans “very soon, certainly within the next couple weeks.”

Dorgan, who has written two books critical of national policy on trade and financial regulation, said he has received an offer to write two more books. He said he wants to work on energy and technology issues but doesn’t see himself working as a lobbyist.

He also said he looked forward to having a less regimented schedule.

“I don’t know that this is the end of my public service. We’ll see. Who knows whether there are other opportunities,” Dorgan said. “But at least at this point, I really would like to do some other things.”

Dorgan’s decision means Democrats will have to defend open Senate seats in at least four states in what could be a challenging election year. They now hold an effective 60-40 majority in the Senate — enough to break Republican filibusters — if they and the chamber’s two independents, who align themselves with Democrats, stick together.

North Dakota Republicans say President Barack Obama’s health care initiative and support for energy regulation have made things difficult for the state’s all-Democratic congressional delegation — Dorgan, Sen. Kent Conrad and Rep. Earl Pomeroy.

“They have a millstone wrapped around their neck that is almost an impossible thing to defend,” said Public Service Commissioner Kevin Cramer, a Republican who is considering making a bid for the U.S. House this year. Cramer twice ran unsuccessfully against Pomeroy in the 1990s.

Pomeroy announced Wednesday in Fargo that he would seek a 10th term. Conrad is not up for re-election until 2012.

Rumored as a possible Senate candidate, Pomeroy said he has no interest in giving up his seniority in the House and leaving North Dakota with two freshmen lawmakers.

“I look at the Senate from across the Capitol in the U.S. House. It looks to me like that place gets more and more screwed up every day,” Pomeroy said.

Dorgan said criticism of the president’s agenda was not a reason he decided against seeking re-election.

“I really believe that this president inherited the biggest batch of trouble of any president since the 1930s. This economy was in desperate trouble,” Dorgan said. “He is slowly, but surely, trying to move this country to higher ground.”

Dorgan turns 68 in May. He said his health is excellent and he weighs the same as he did when he was elected to the U.S. House in 1980. He was elected to the Senate 12 years later.

“It’s very hard to get to the United States Senate,” Dorgan said. “But in addition to it being hard to get here, it’s also very hard for people to leave … I’d rather they wonder why I left too soon than stayed too long.”

The North Dakota Democratic state party chairman, Mark Schneider, said Wednesday he expected several Democrats to be interested in the Senate seat.

A supporter of one potential candidate, Heidi Heitkamp, a former Democratic attorney general and tax commissioner, set up a Facebook page late Tuesday urging her to run. It had drawn more than 700 supporters by early Wednesday afternoon.

Heitkamp did not respond Wednesday to phone and e-mail messages seeking comment. She lost to Hoeven in the governor’s race in 2000.

Broadcaster Ed Schultz, a former Fargo radio talk show presenter who hosts MSNBC’s liberal “The Ed Show,” told MSNBC on Wednesday that he had been approached by a top North Dakota legislator to consider a Senate bid.

Schultz said he was “flattered” and “honored” but “I can’t say that I’m even considering it right now … I’m in a different place right now. So we’re a long way from any consideration.”

Schneider and Joe Aronson, director of the state Democratic Party, said Wednesday they had not approached Schultz.

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Associated Press Writer Ken Thomas in Washington contributed to this report.