WASHINGTON - A day after her nomination ran into trouble in the Senate, President Obama's pick to head the Social Security Administration passionately defended her integrity, her long career in government, and her handling of a troubled computer project she inherited from a predecessor.

"I've always met the highest ethical standards," Carolyn W. Colvin said Thursday in an interview. "I've worked in government my entire life. There's never been a suggestion, personal or professional, of any wrongdoing.

"I'm certainly not ending my career with that," said Colvin, 72. "I came out of retirement to help this organization, not hurt it."

Nominated in June

Obama nominated Colvin in June to a six-year term as commissioner of the agency. She has been acting commissioner since February 2013.

A group of Republican senators plans to try to block Colvin's nomination while investigators look into a $300 million computer project that doesn't work. In a letter to Colvin, all 11 Republicans on the Senate Finance Committee said there was evidence that Social Security officials had misled Congress and investigators about problems with the project.

The senators wrote that they couldn't let a nomination proceed "as long as the specter of a potential criminal investigation surrounds the nominee," that person's inner circle, or both.

Racked by delays

Six years ago, Social Security embarked on an aggressive plan to replace outdated computer systems overwhelmed by a flood of disability claims. But the project has been racked by delays and mismanagement, says an assessment commissioned by the agency over the summer.

The project is still in the testing phase, and the agency can't say when it will be operational or how much it will cost.

Colvin was adamant during the interview that she did not know of anyone in the agency misleading Congress or investigators.

"I haven't been interviewed or given specifics," she said, "and I think that it would be inappropriate for me to say a whole lot more."