Democrats have criticized Burns for his connection to the lobbyist at the center of a federal probe that has entangled at least a half dozen lawmakers and Bush administration officials. Earlier this week, a spokesman for Burns said the senator would not return the money because it had already been spent.
"The contributions given to my political committees by Jack Abramoff and his clients, while legal and fully disclosed, have served to undermine the public's confidence in its government," Burns said.
In a statement, Burns called on other members of Congress to return their own donations from the lobbyist.
"This is an important step that all public officials should take in order to renew the faith of Montanans, and all Americans, in their government," he said. "We can and must set a higher ethical standard."
The Associated Press has reported that in 2001 the Montana Republican and his staff met Abramoff's lobbying team on at least eight occasions and collected $12,000 in donations around the time that Burns took legislative action favorable to Abramoff's clients in the Northern Mariana Islands.
Donations to Burns included money directly from Abramoff and a key garment company executive in the islands. The executive was part of the coalition paying Abramoff's firm to fend off stronger U.S. regulations on the Pacific islands.
The Justice Department is investigating whether Abramoff, already charged with fraud in a separate Florida case, won any undue influence through donations and favors.
Burns faces re-election next year and the link to Abramoff has created a flurry of headlines in his home state. The senator, first elected in 1988, won a third term with just 51 percent of the vote in 2000.
Burns has said he hasn't been contacted by federal investigators in the Abramoff inquiry or received any subpoenas. Last month, Burns wrote to Attorney General Alberto Gonzales, urging that his conduct be reviewed so he could be cleared of wrongdoing.
"I welcome your thorough and expeditious review of this matter so that it may be disposed of officially once and for all and these outrageous and wrongful allegations may be put to rest before we get into the 2006 re-election cycle," Burns wrote.
In 2001, Burns served on the Senate Energy and Natural Resources Committee, which was considering legislation the Marianas opposed.
On May 23 of that year, Burns voted against a bill in the Senate Energy Committee that would have phased out a nonresident contract worker program benefiting the Marianas' garment industry. The committee approved the bill, but it never saw action on the Senate floor. In 1999, it had moved through the same committee by voice vote without objections from Burns.
Burns' office told The Associated Press that he could not recall why he didn't object to the bill in 1999 but that his opposition in 2001 was prompted by a report indicating changes to immigration laws could hurt the islands' economy. He said it wasn't influenced by Abramoff or any donations.
He also ran a Senate appropriations subcommittee that controlled spending for the Interior Department, which regulates U.S. territories, including the islands, and American Indian programs. Burns and North Dakota Sen. Byron Dorgan, who is the top Democrat on that subcommittee, wrote a letter in 2002 backing an Indian school building program sought by Abramoff's tribal clients, and helped arrange congressional funding for it.
Dorgan said Dec. 12 that he is returning $67,000 in donations from the lobbyist and his associates.
Burns said he would return all of the donations to their original donors, with the exception of those from Abramoff and his associates.
"I have instructed my staff to work with the Montana Wyoming Tribal Leaders Council to identify an appropriate Native American charitable entity to which the contributions received directly from Mr. Abramoff and his associates may be donated," Burns said.