WASHINGTON - Sen. John Ensign (R., Nev.) stepped down from his party leadership post yesterday, one day after acknowledging an extramarital affair with a woman on his campaign staff.

The woman confirmed her involvement with the conservative Republican and lamented his decision to "air this very personal matter."

Ensign, 51, a married father of three, has said he intends to remain in the Senate. But his fall from grace is a further blow for Republicans struggling to recover from recent election reversals as well as from the political defection of Sen. Arlen Specter of Pennsylvania.

Ensign's announcement also added to an appearance of disarray for the party in Nevada, where GOP Gov. Jim Gibbons has been embroiled in nearly nonstop controversy throughout his term.

Ensign offered to resign as head of the Republican Policy Committee in a phone call with Senate Minority Leader Mitch McConnell (R., Ky.), who accepted the resignation.

Ensign is a member of the Christian ministry Promise Keepers and has championed causes pushed by the GOP's conservative religious base while seeking to raise his political profile for a possible presidential campaign.

His position within the Republican leadership was a reflection of his popularity among the rank-and-file, but not a single Republican senator came to his public defense in the first hours after his announcement Tuesday.

In that news conference, Ensign said his affair last year was "the worst thing I have ever done in my life."

His office said the affair was consensual and took place from December 2007 through August 2008. It said the campaign aide was married to an official Senate staffer who worked for Ensign.

Neither Ensign nor his aides would name the woman or her husband, though Ensign described them as good friends. But the couple, Cindy and Doug Hampton, identified themselves yesterday through their attorney.

An Associated Press review of federal records shows that Cynthia Hampton, 46, was on the payroll of Ensign's Battle Born Political Action Committee at $1,385.24 a month until she was appointed treasurer, and her salary was doubled to $2,771.50 in February 2008.

Her salary also doubled - from $500 a month to $1,000 - at Ensign's campaign committee, where she was treasurer, starting about the time the affair began.

Records also show that Doug Hampton earned $13,555 a month as an administrative assistant in Ensign's Senate office. He was paid $19,679 for his final month of employment, and was off the payroll on May 1, 2008, according to Senate records.

Additionally, the National Republican Senatorial Committee made twice-monthly payments, generally $500 apiece, to Brandon Hampton, who Republican officials said was the couple's son. The payments began in March 2008 and ended in August.

The couple's lawyer, Daniel Albregts, said in a statement that "in time, the Hamptons will be ready and willing to tell their side of the story."