Susan Ralston, special assistant to President George W. Bush, submitted a resignation letter to him less than five weeks before the Nov. 7 elections.
"She did not want to be a distraction to the White House at such an important time and so we have accepted her resignation," White House deputy press secretary Dana Perino said.
"We support her decision and consider the matter closed," Perino said.
Critics have pointed to Ralston as evidence that Rove — and thus Bush — are possibly closer to Abramoff than the White House has acknowledged. Ralston was Abramoff's administrative assistant at his lobbying firm and, after Bush took office, assumed the same post with Rove.
The Federal Bureau of Investigation has been pursuing leads about Abramoff's access to the White House and whether he was able to help lawmakers get Bush administration backing for their bills, according to people familiar with the direction of the investigation.
A congressional report released last month showed that Abramoff had hundreds of contacts with White House officials over three years, including 10 with Rove. While Abramoff provided officials with meals or tickets to sporting events, the report said his efforts to influence presidential appointments and nominations "were often not successful."