The investigation of powerful GOP lobbyist Jack Abramoff and his business associate Michael Scanlon led to partisan sparring yesterday as a Senate committee prepared to begin a hearing today into the millions of dollars in lobbying and public relations fees the pair were paid by Indian tribes that operate gambling casinos.

Democrats contended that House Majority Leader Tom DeLay's ability to campaign for fellow Republicans has been damaged by news reports on the business dealings of Scanlon, a former spokesman for the Texas Republican, and Abramoff, and the indictment last week of three DeLay aides on charges of illegally raising political money.

Greg Speed, spokesman for the Democratic Congressional Campaign Committee, said: "This is another example of the growing ethical cloud surrounding Tom DeLay and his political operation. It's clearly having an impact on his ability to travel and support Republican campaigns. Just [Monday], DeLay had to go into virtual hiding while campaigning for Billy Tauzin in Louisiana."

Speed cited an article in Tuesday's New Orleans Times-Picayune headlined "DeLay's stumping for Tauzin is scaled back after scandal." The article said DeLay's appearance "was scaled back to a 11/2-hour private fund-raiser" and quoted a Tauzin spokesman as saying it was because the majority leader was pressed for time. The spokesman denied any connection with the indictments or other controversies.

But aides to DeLay and House Speaker J. Dennis Hastert (R-Ill.), both of whom have had extensive dealings with Abramoff, said the hearings will not hurt the GOP's top House leaders.

John Feehery, spokesman for Hastert, said today's hearing before the Senate Indian Affairs Committee "will hurt [Abramoff and Scanlon]; it won't hurt us. This is not behavior we condoned."

Similarly, an aide to DeLay, who did not want to be identified, said that no one in the legislator's office has had contact with Scanlon for the past four years. A statement from DeLay said, "What I can tell you is that if anybody is trading on my name to get clients or to make money, that is wrong and they should stop it immediately."

The Indian Affairs Committee and a federal grand jury are investigating at least $50 million in lobbying and public relations fees Abramoff and Scanlon garnered from Indian tribes that operate gambling casinos. The FBI and a task force of five federal agencies are investigating campaign contributions the two men directed the tribes to make to members of Congress, and whether tribal funds were misused in the contracts the two men obtained or the fees they collected, government sources said.

The Indian Affairs Committee is seeking testimony from both men today but may not be able to question either one.

Tribal officials have told The Washington Post that Abramoff, whose lobbying fees must be disclosed to the public, encouraged them to hire Scanlon's firms for large amounts of money that did not have to be publicly revealed. Senate investigators discovered in March that Scanlon paid Abramoff at least $10 million. Neither the tribes nor Abramoff's former lobbying firm, Greenberg Traurig, was aware of the payments, they have said.

E-mails obtained by The Post show that Abramoff and Scanlon worked with conservative religious activist Ralph Reed to help Texas shut a casino operated by the Tigua Indians in 2002, then persuaded the tribe to pay them $4.2 million to lobby Washington lawmakers to reopen it.

Peter Mirijanian, a spokesman for Abramoff, said late yesterday that Abramoff plans to assert his Fifth Amendment right against self-incrimination today rather than answer questions posed by the Indian Affairs Committee. But Abramoff's lawyer, Abbe D. Lowell, said last night that a final decision had not been made.

As of last night, Scanlon's appearance was in doubt because U.S. marshals have not been able to locate him to serve him with a subpoena, according to congressional sources. Scanlon's lawyers, Stephen L. Braga and Plato Cacheris, did not return phone calls seeking comment yesterday. Braga informed the committee last week that he has not been authorized to accept service of a subpoena for Scanlon's testimony, the congressional sources said. Cacheris is out of the country, his office said yesterday.

Led by Sens. Ben Nighthorse Campbell (R-Colo.) and John McCain (R-Ariz.), the committee has obtained the cooperation of several tribes and subpoenaed records from banks, Scanlon's public relations companies and Greenberg Traurig. Abramoff resigned under pressure from the firm in March after the firm said it had become aware of his involvement in certain "unacceptable" transactions.

The panel is expected to reveal e-mails between the two men showing how they obtained tens of millions of dollars in tribal business. Among those scheduled to testify are Bernie Sprague, sub-chief of the Saginaw Chippewas of Michigan, and Richard Milanovich, chairman of the Agua Caliente tribe in Palm Springs, Calif. Both men opposed hiring Abramoff and Scanlon but were outvoted.

Abramoff was defended earlier this week by Grover Norquist, a conservative activist who heads Americans for Tax Reform, a Washington anti-tax group. He told National Public Radio that part of the controversy may stem from a rivalry between Abramoff and lobbyist Scott Reed, a McCain backer who began working as a lobbyist for the Saginaw Chippewas earlier this year, after the tribe fired Abramoff.

Norquist has been close to Abramoff and Ralph Reed since their days as college Republicans. Tribal representatives have told The Post that Abramoff urged them to contribute to Americans for Tax Reform. The Saginaw Chippewas gave the group $25,000 on Nov. 13, 2002, according to a tribal representative. The Agua Caliente also donated about $20,000 to the group, according to sources close to the tribe.

The Senate Indian affairs panel will investigate Jack Abramoff's lobbying fees from tribes.