"The document released by my office yesterday went too far and I want to convey to you my personal regrets," Reid said in a letter.
"I am writing to apologize for the tone of this document and the decision to single out individual senators for criticism in it."
Reid came under attack Wednesday over the report, which was issued by his staff on Senate letterhead, even as he and fellow Democrats released ethics overhaul proposals.
"Researching, compiling and distributing what amounts to nothing more than a campaign ad on the taxpayers' dime raises serious ethical questions," said Sen. John Cornyn, R-Texas, one of the lawmakers named.
The 27-page report criticized Republican lawmakers over their ties to disgraced ex-lobbyist Jack Abramoff, questionable campaign contributions and other issues.
Meanwhile, the head of the Republican Party said GOP lawmakers who are guilty of wrongdoing should expect to be punished whatever their political affiliation.
"The public trust is more important than party," said Ken Mehlman, the Republican National Committee chairman. "Which is why the first solution to the problem is rooting out those who have done wrong, without regard to party or ideology."
Mehlman's comments were in a speech that he planned to deliver Friday to the annual winter meeting of the Republican National Committee. The Associated Press obtained a copy of the speech.
The Abramoff investigation threatens to ensnare at least a half dozen members of Congress of both parties and Bush administration officials. Abramoff, who has admitted to conspiring to defraud his Indian tribe clients, has pleaded guilty to corruption-related charges and is cooperating with prosecutors.
With the midterm elections 10 months away, Democrats have tried to link Abramoff to Republicans, the main recipients of his largesse.
Two senior Republicans have already taken a fall because of their ties to Abramoff.
Former Majority Leader Tom DeLay, R-Texas, announced after Abramoff's guilty plea that he would not try to regain the post he relinquished after being indicted on separate campaign finance charges in Texas. Rep. Bob Ney, R-Ohio, temporarily stepped down as chairman of the House Administration Committee.
Mehlman said the GOP must earn the public's trust by recommitting itself to reform.
Responding to the influence-peddling scandal, Republicans and Democrats have introduced similar ethics reform packages.
Mehlman said the response to the scandal should not be "partisan hypocrisy." He criticized Reid for calling the Abramoff affair a Republican scandal. Reid has come under fire for his own ties to Abramoff, including accepting money from Abramoff's tribal clients.
Four Senate Democrats sent a letter to senior administration officials on Thursday calling on them to disclose any dealings with Abramoff such as meetings, memos or favors.
The Democrats said the record should be "cleared and that any contact you or others in the administration have had with Mr. Abramoff be fully explained to the American people."