OMAHA, Neb. (AP) - Democratic Sen. Ben Nelson said Wednesday he doesn't think his decision not to run for a third term next year will automatically give the seat to Republicans, who already hold the other four spots in Nebraska's congressional delegation.

Nelson told The Associated Press that the timing of his announcement this week shouldn't be a problem for Democrats in 2012.

"There has always been plenty of time for the campaign. If it's not too late for Republicans to get in, why is it too late for Democrats to get in?" Nelson said.

Other Democrats have acknowledged they face an uphill battle to keep Nelson's seat away from the GOP, which must pick up four Senate seats in next year's election to regain control of the chamber.

The Republican primary field already is crowded with Nebraska Attorney General Jon Bruning, state Treasurer Don Stenberg, state Sen. Deb Fischer, and investment adviser Pat Flynn, and no Democrats are lined up to take Nelson's place in the conservative state.

Nelson said he's confident he still could have won re-election because his poll numbers have improved despite being hammered by conservatives for supporting the federal health care overhaul. He also said national GOP leaders seemed concerned because they recently tried to recruit Republican Gov. Dave Heineman as a candidate.

"I think that says a lot about what people thought about my chances of winning from the other side," Nelson said. "I think they were worried about that."

Nelson declined to speculate about Democrats who might seek his seat, or say whether he would use any of the campaign cash he'd amassed in support of other candidates.

The former governor and two-term senator had more than $3 million in campaign money on hand last month, about twice his nearest competitor. Federal election rules allow him to give at least some of that money to other candidates and political action groups or donate it to charity. But any funds donated specifically for the 2012 general election campaign will have to be returned.

Melanie Sloan, executive director of Citizens for Responsibility and Ethics in Washington, said most retiring politicians hang onto their campaign money and donate it to candidates later, especially if they intend to become lobbyists.

"Money in Washington helps buy you influence, and now Ben Nelson has $3 million to spread around," said Sloan, who leads the nonpartisan watchdog group.

Nelson survived his nearly two decades representing his heavily conservative state by carving a path down the political center, and said Wednesday he thinks there still is room for moderate politicians in Washington. But he said the current political climate makes bipartisanship more difficult.

"There's no doubt about it because we've seen a great deal of polarization in the country," he said. "And the polarization in Washington is immense," Nelson said, "but on the right issues you can still work with people."

Nelson, 70, said he consulted family, friends and current and former Senate colleagues before deciding that he wanted to be free to go hunting, spend more time with his family, travel and pursue other opportunities while he's still in good health.

"For 20 years, I've been doing things on behalf of the people of Nebraska and putting things off," he said. "There comes a time when you have to make that decision, do you continue to put things off and do what you've been doing?"