Standing before Judge Ellen S. Huvelle, Ney pleaded guilty to conspiracy and making false statements. He acknowledged taking money, gifts and favors in return for official actions on behalf of Abramoff and his clients.
Ney did not immediately resign from Congress, but said in a statement that he will step down "in the next few weeks." Republican and Democratic leaders quickly vowed to expel him if he doesn't. The White House also called for Ney's resignation.
Beleaguered Republican leaders, struggling to overcome fallout from a separate scandal involving former Rep. Mark Foley and teenage male pages, said they would make Ney's ouster the "first order of business" in a session after the Nov. 7 elections.
The scandal is likely to reinforce Democrats' contention in the campaign leading up to the elections that the ruling Republicans are corrupt and do not deserve to retain control of the House of Representatives and the Senate. There also could be difficulties for Republican candidates in Ney's home state of Ohio.
"I never intended my career in public service to end this way, and I am ashamed it did," Ney said in a written statement issued moments later.
The 52-year-old lawmaker faces a maximum of 10 years in prison. Huvelle said prosecutors had agreed to recommend a term of 27 months, and said federal guidelines suggest a fine of between $5,000 and $60,000.
As to why he's not resigning now, several officials have said the congressman is financially strapped and needs his $165,200 annual paycheck and benefits as long as he can continue to receive them.
Ney's lawyer, Mark Touhey, told the judge he would resign before sentencing on Jan. 19. The House Republican leader, Dennis Hastert, and other Republican leaders said he would be gone far more quickly than that.
Rep. Nancy Pelosi, the Democratic leader, called Ney's guilty plea "further proof that the Republican culture of corruption has pervaded Congress."
Ney is the latest in a string of once-influential men convicted in a scandal that so far has caught several lobbyists and two members of the Bush administration.
Abramoff, the Republican super-lobbyist, admitted guilt in January after secretly cooperating with prosecutors for weeks.
Two former aides to Tom DeLay, the former House majority leader, have also pleaded guilty, as has Ney's former chief of staff.
Additionally, Roger Stillwell, a former Interior Department official, pleaded guilty in August to a misdemeanor charge for not reporting tickets he received from Abramoff.
And former White House official David Safavian, who had been the Bush administration's top procurement official, was convicted of covering up his dealings with Abramoff. He is scheduled for sentencing on Oct. 27.
Ney confessed his wrongdoing in a federal courthouse a few blocks from the Capitol building, where until recently he wielded a committee chairman's gavel.
The first charge accused Ney of conspiring to commit "honest services" fraud, a combination of mail and wire fraud often used in public corruption cases. The second count charges Ney with not revealing his gifts from Abramoff on financial disclosure forms.
Ney acknowledged accepting all-expense-paid and reduced-price trips to play golf in Scotland in August 2002, to gamble and vacation in New Orleans in May 2003 and to vacation in New York in August 2003. The total cost of all the trips — in which others, including some aides, participated — exceeded $170,000, prosecutors said.
Ney also admitted accepting meals and sports and concert tickets for himself and his staff.
During his time in Congress, Ney built up goodwill back home for his responsiveness and visibility in a sprawling, conservative region of mines, farms and Rust Belt towns in eastern Ohio.
He also drew some attention for his role in helping get french fries renamed freedom fries in House cafeterias three years ago to protest French opposition to the U.S.-led invasion of Iraq.
In another Abramoff-related development, a new Senate report said five nonprofit groups linked to the disgraced lobbyist may have broken laws and endangered their tax-exempt status.
Among the groups named as possibly taking money from Abramoff clients and funneling it into his lobbying efforts on their behalf were Americans for Tax Reform, Citizens Against Government Waste and the Council of Republicans for Environmental Advocacy.
Tax-exempt groups are barred by law from being paid to lobby or do public relations.
Americans for Tax Reform is headed by Grover Norquist, a key ally of President Bush and a longtime associate of Karl Rove, the president's chief political adviser.
The report by the Senate Finance Committee said Norquist's group accepted $1.5 million from the Mississippi Band of Choctaw Indians, one of Abramoff's clients. More than two-thirds of that money was then passed to Christian Coalition founder Ralph Reed as part of Abramoff's lobbying efforts to block a rival tribe's proposed casino in Alabama.
Norquist's group and a second organization cited in the report denied any wrongdoing. They also questioned the timing of the report's release so close to Nov. 7 elections in which Republicans are trying to return their control of Congress.
"This is political nonsense put out by the Democrats in an inappropriate attempt to influence the election," said John Kartch, communications director for Americans for Tax Reform.
David Williams, a vice president of Citizens Against Government Waste, said it was "kind of suspicious that three weeks before an election, this comes out."
The 600-page report was prepared by the finance committee's Democratic staff. Majority Republicans, however, had agreed to its release and joined with Democrats in issuing subpoenas for documents and e-mails cited in the report.