By Bill Trott

WASHINGTON (Reuters) - Republicans in the U.S. Congress are under a "reign of terror" imposed by the party's conservative wing that also has pushed presumptive Republican presidential nominee Mitt Romney to the right, President Barack Obama's senior campaign strategist said on Sunday.

David Axelrod, in an interview on CNN's "State of the Union" program, cited the Obama administration's plans for immigration reform as an example of Republican intransigence in Congress.

The political process in Washington should not be "monolithic opposition to everything the chief executive wants to do as a political strategy," Axelrod said, adding that an "implacable group of Republicans" had blocked any possibility of immigration reform.

"I think there are a lot of Republicans in Congress who want to cooperate ... but they're in the thralls of this reign of terror from the far right that has dragged the party to the right," he said.

"Governor Romney and the party have gone way off to the right," he added.

On NBC's "Meet the Press," Axelrod said that if Obama is re-elected, some Republicans would be more willing to work with him.

Axelrod said Romney, the former Massachusetts governor in line to be the Republican challenger to Obama's re-election in the November 6 election, has nothing new to offer voters.

"People don't know Mitt Romney very well," he said on CNN. "They see a businessman. They hope he has new ideas. When they find out what his ideas are, slashing taxes at the top for the very wealthy ... they're going to think, 'This is very familiar. We've tried this. This was a big failure.'"

Axelrod said Romney's campaign for the Republican nomination had been a negative one, based on attacking his opponents rather than spelling out ideas.

"When he does, I think people are going to judge them for what they are, which is backward-looking and a repeat of what got us into this mess in the first place," he added.

(Editing by Will Dunham)