WASHINGTON, April 11 — Five years after the Bush administration began a crackdown on voter fraud, the Justice Department has turned up virtually no evidence of any organized effort to skew federal elections, according to court records and interviews.

Although Republican activists have repeatedly said fraud is so widespread that it has corrupted the political process and, possibly, cost the party election victories, about 120 people have been charged and 86 convicted as of last year.

Most of those charged have been Democrats, voting records show. Many of those charged by the Justice Department appear to have mistakenly filled out registration forms or misunderstood eligibility rules, a review of court records and interviews with prosecutors and defense lawyers show.

In Miami, an assistant United States attorney said many cases there involved what were apparently mistakes by immigrants, not fraud.