Sen. John McCain (R-Ariz.) began making inroads this week into the investigation of the multimillion-dollar lobbying and public relations deals two Republican activists struck with American Indian tribes.

Aides for McCain, who is coordinating the investigation with Indian Affairs Chairman Ben Nighthorse Campbell (R-Colo.), met Tuesday with officials from Greenberg Traurig, the law firm that recently fired lobbyist Jack Abramoff after some of his clients began questioning the $15 million in fees he charged a few tribes in recent years.

Brandishing letters from two tribes asking Greenberg Traurig to waive any confidentiality claims, McCain’s staff appears to have secured a tentative agreement with the firm to begin receiving large amounts of documents related to Abramoff’s dealings with the tribes.

“We are laying the groundwork for getting a lot of documents very quickly,” said one Senate source familiar with the meeting.

McCain, in a brief interview Tuesday, cautioned that the most important documents had yet to be reviewed.

“We’ve got a lot of work to do,” he said, guessing that his investigation would produce a hearing later in the spring or early in the summer.

As the investigation has kicked into a higher gear, more lawyers have become involved in the case. The meeting between McCain’s staff and officials from Greenberg Traurig took place at the law firm Williams and Connelly, which has been retained by Greenberg to handle all external investigations related to the firm’s three-year run with Abramoff.

A representative at Williams and Connelly declined to talk about the case.

After they forced Abramoff out, which followed media reports in Washington about the tribal fees, Greenberg Traurig officials hired Henry Schuelke III to conduct an internal investigation of Abramoff’s actions and determine whether the firm should take any actions against its former employee. Schuelke is one of Washington’s top defense lawyers on financial criminal matters.

Abramoff signed a deal Tuesday to work as a consultant for another lobbying firm, Cassidy and Associates.

In addition to Abramoff, the Senate investigation is focusing on Michael Scanlon, the public relations official whom Abramoff pointed tribal officials to for handling grassroots and marketing business. Scanlon, who made at least twice as much money as Abramoff over a three-year period, $31 million, has retained two law firms, according to a source familiar with the Senate probe.

In addition to Baker Botts, the firm founded by the family of former Secretary of State James Baker, Scanlon has also brought on Plato Cacheris, one of the most flamboyant criminal defense lawyers in the political world.

Cacheris has a roster of former clients that spans decades of Washington scandals, including Monica Lewinsky and Fawn Hall.

Calls to representatives at Baker Bott and Cacheris, who now works at Baker and McKenzie, were not returned Tuesday.

Once McCain’s staff can start getting documents from Greenberg Traurig, aides say the next step will be to plan trips to at least two of the tribes that are so far cooperating with the investigation, the Saginaw Chippewa Indian Tribe of Michigan and the Coushatta Tribe of Louisiana.

Those two tribes have sent letters to Greenberg Traurig and McCain indicating they want to fully cooperate with any investigation into the lobbying fees, waiving confidentiality privileges as related to McCain’s investigation. The Coushattas have been in the midst of an internal political war of its tribal council, with the anti-Abramoff wing of the council apparently wielding control for the moment.

As long as that wing of the council holds control, McCain’s panel expects full cooperation and the tribe’s contract with Greenberg Traurig will be terminated.

From 2001 through 2003, the Coushattas and the Saginaws paid more than $10 million combined in lobbying fees for Abramoff’s work at Greenberg Traurig.

McCain questions what work Abramoff provided that warranted such high fees, contending that there are many services that could have instead been provided to lower income members of the tribes — a claim some new tribal leaders back up.

“It is vital to the Coushatta people that all possible disclosures be made so that tribal members can have what is rightfully theirs in the future,” wrote Harold John, a member of the tribal council, to Greenberg Traurig officials.

McCain said he has met resistance from at least one of Abramoff’s clients, the Mississippi Band of Choctaw Indians, which paid out $5.3 million for Abramoff’s work the past three years.

In a letter that has remained confidential at the Choctaw’s request, the tribe informed the Senator that they did not expect to cooperate with his investigation and that it had no problems with Abramoff’s work over the years.

News reports have indicated that local offices of the FBI have sent officials to the Saginaw Chippewas regarding investigations into their lobbying contracts, as well as conducted meetings with local law enforcement officials in Louisiana regarding the Coushattas.