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.