WASHINGTON, Nov. 21 - Michael Scanlon, a former business partner of the lobbyist Jack Abramoff and a former top aide to Representative Tom DeLay, pleaded guilty on Monday to conspiring to bribe a member of Congress and other public officials.
Mr. Scanlon also agreed to repay $19.6 million to his former Indian tribe lobbying clients.
He acknowledged in a plea agreement that he and Mr. Abramoff, identified in the court papers as "Lobbyist A," agreed to make lavish gifts to public officials, including all-expense-paid trips to Europe and the Super Bowl, in exchange for official actions.
Federal law enforcement officials portrayed the plea bargain, under which Mr. Scanlon faces up to five years in prison, as an important development in the larger criminal investigation of Mr. Abramoff, who has been under scrutiny by a grand jury here for more than a year.
The investigation, which initially centered on accusations that Mr. Abramoff had defrauded tribal casinos of tens of millions of dollars in lobbying fees, has created alarm on Capitol Hill, where the lobbyist and his junior partner, Mr. Scanlon, claimed friendships among the Republican leaders of Congress.
Prosecutors have not named any of the public officials who were the targets of Mr. Scanlon's scheme.
But court papers in the case filed Monday and last week singled out one member of Congress - "Representative No. 1" - as a focus of Mr. Scanlon's illegal lobbying, asserting that the lawmaker accepted gifts, including a 2002 golf trip to Scotland and regular meals at Mr. Abramoff's restaurant, "in exchange for a series of official acts and influence."
Representative Bob Ney, an Ohio Republican and chairman of the House Administration Committee, has acknowledged that he is the lawmaker, while saying there was no quid pro quo with Mr. Abramoff or Mr. Scanlon. Mr. Ney, who was subpoenaed this month by the grand jury investigating Mr. Abramoff, has said he was "duped" by the lobbyists.
Brian J. Walsh, the lawmaker's spokesman, said, "All this plea agreement shows is that Mr. Scanlon had a deliberate, secret and well-concealed scheme to defraud many people, and it appears, unfortunately, that Representative Ney was one of the many people defrauded."
Mr. Scanlon, 35, a longtime Republican operative in the capital, said little during the hearing Monday in Federal District Court here.
"Guilty, Your Honor," he replied calmly when asked by Judge Ellen Segal Huvelle for his plea.
Under the agreement with the Justice Department, Mr. Scanlon pleaded guilty to one count of conspiracy to violate a series of criminal laws, including those against bribery, and pledged to cooperate with the Justice Department's investigation of Mr. Abramoff and others.
At a news conference after the hearing, Mr. Scanlon's lawyer, Plato Cacheris, stood alongside his client and said Mr. Scanlon was "obviously regretful" about the fraud committed against the Indians, who paid Mr. Abramoff and Mr. Scanlon more than $80 million in fees.
Asked if he expected the investigation to bring many members of Congress under scrutiny, Mr. Cacheris replied, "I would rather not comment on that."
Asked if Mr. Scanlon had information that would bring Mr. DeLay under investigation, the lawyer replied, "You'll have to ask his lawyers."
Mr. Scanlon, tanned and grinning, referred questions to his lawyer. Asked why he appeared so relaxed and why he was smiling so broadly, he replied, "I always smile."
There was no suggestion in the Justice Department's paperwork that the $19.6 million in restitution, reflecting Mr. Scanlon's profits from four of the Indian tribes he defrauded, would leave him destitute.
His lawyers said Monday that Mr. Scanlon now lived in Rehoboth Beach, Del., a resort town on the Atlantic coast, and continued to work as a consultant, sometimes traveling abroad on business. Judge Huvelle did not seize Mr. Scanlon's passport, instead ordering him to provide prosecutors with two weeks' notice of any foreign travel.
Before turning to lobbying in 2000, Mr. Scanlon was press secretary to Mr. DeLay, the former House majority leader, who is under indictment in Texas on unrelated charges of violating state election laws.
The plea agreement released Monday offered new details of many of the accusations against Mr. Scanlon.
It said that beginning in January 2000, Mr. Scanlon and Mr. Abramoff conspired to begin offering a "stream of things of value to public officials in exchange for a series of official acts and influence and agreements to provide official action and influence."
"Those things of value included, but are not limited to, travel, golf fees, frequent meals, entertainment, election support for candidates for government office, employment for officials and relatives of officials and campaign contributions," it said.
For Mr. Ney and his staff, the agreement said, the gifts included "all-expense-paid trips, including a trip to the Commonwealth of the Northern Mariana Islands in 2000, a trip to the Super Bowl in Tampa, Fla., in 2001, and a golf trip to Scotland in 2002."
Mr. Ney and his staff also took "numerous tickets for entertainment, including concerts and sporting events in the Washington, D.C., area," and were given "box suites and food at various sport and concert venues and at a restaurant in the Washington, D.C., area."
The restaurant was Signatures, which Mr. Abramoff once owned and which he had long used as a second office, wining and dining members of Congress. The plea agreement said Mr. Ney and his staff received "regular meals and drinks" at the restaurant.
As a result of what prosecutors described as Mr. Scanlon's "course of conduct," Mr. Ney and his House staff offered "their official positions and influence" to help Mr. Scanlon, Mr. Abramoff and their lobbying clients, including directing a House contract for wireless telephones to one of Mr. Abramoff's lobbying clients.
Mr. Walsh, Mr. Ney's spokesman, said in a statement that the plea bargain was wrong in many of its details. "Whenever Representative Ney took official action - actions similar to those taken by elected representatives every day as part of the normal, appropriate government process - he did so based on his best understanding of what was right and not based on any improper influence," the statement said.