WASHINGTON — Lobbyist Jack Abramoff, whose fees to Indian gaming tribes propelled his law firm to the top lobbying ranks, resigned Wednesday as a Senate investigation prepares to turn a spotlight on more than $45 million in fees he and a public relations executive have garnered from four tribes.

"Greenberg Traurig has accepted Jack Abramoff’s resignation from the firm, effective today. Last Friday, Feb. 27, 2004, Mr. Abramoff disclosed to the firm for the first time personal transactions and related conduct which are unacceptable to the firm," said Richard Rosenbaum, the firm’s managing director.

Abramoff and Michael Scanlon, a former spokesman for House Majority Leader Tom DeLay, R-Texas, signed up newly wealthy tribes for lobbying and public affairs work during the past three years that cost as much as some of the nation’s biggest corporate interests pay to influence public policy. Abramoff also advised the tribes to give $2.9 million in federal political contributions, two-thirds of it to Republicans.

The huge fees and political contributions have spawned battles within the tribes, with some members complaining that they cannot understand why a few tribal leaders have spent such sums for so little in return. Abramoff also advised the tribes to give hundreds of thousands of dollars to obscure groups that appear to have no connection to Indian concerns, including one — American International Center — that has been one of Greenberg Traurig’s largest clients.

Scanlon, responding earlier this week to e-mailed questions about American International Center, which is located at an address associated with him in Rehoboth Beach, Del., said the center was a firm he had created. Scanlon had agreed to an interview Wednesday morning but canceled it abruptly.

Sen. John McCain, R-Ariz., and the Senate Indian Affairs Committee this week launched an investigation into Abramoff and Scanlon’s work for the tribes after their activities were detailed Feb. 22 in a Washington Post story. A congressional aide familiar with the progress said Wednesday that McCain "is committed to going forward with the investigation."

Rosenbaum said Greenberg Traurig has retained outside lawyer Henry Schuelke to conduct an internal investigation. While Abramoff’s fees of $180,000 a month to each of four tribes were the subject of much notice in the lobbying world, Rosenberg said he was "not aware of any allegations of impropriety before."

Rosenbaum said he does not know all the facts yet, or whether there was any illegality involved in Abramoff and Scanlon’s activities. Abramoff resigned by mutual agreement with the firm, he said. "We saw enough that we felt we had to have a mutual parting of the ways," he said. "When we see something that we feel we don’t want to have going on here, we act."

Even the huge fees to Greenberg Traurig — totaling $15.1 million, according to federal lobbying reports — are dwarfed by public relations fees charged by Scanlon’s Capitol Campaign Strategies, a firm Abramoff recommended to the tribes for grass-roots work. Scanlon, 33, made more than $30 million, contracts and tribal documents show.